Welding has its own language. Forums, manuals, and certification tests all assume you know these terms. You don’t need to memorize everything at once, but understanding the basics keeps you from getting lost when someone tells you to “run a 3/16 fillet on a 2F tee joint with .035 ER70S-6.”
This list covers 40 terms that show up constantly in beginner welding. They’re organized by category so you can find what you need fast. For a complete reference with deeper technical definitions, see the full welding glossary.
Welding Processes
MIG (GMAW): Metal Inert Gas welding, formally called Gas Metal Arc Welding. A wire electrode feeds continuously through a gun while shielding gas protects the weld from atmospheric contamination. The most beginner-friendly process. “MIG” technically refers to using inert gas (argon), but the term is used broadly for all gas-shielded wire welding, including mixed gases.
TIG (GTAW): Tungsten Inert Gas welding, formally Gas Tungsten Arc Welding. Uses a non-consumable tungsten electrode to create the arc. You feed filler rod with your other hand. Produces the cleanest, most precise welds but has the steepest learning curve.
Stick (SMAW): Shielded Metal Arc Welding. Uses a consumable electrode coated in flux. The flux melts and creates a gas shield and slag layer. Works outdoors, on rusty metal, and in tight spaces. The oldest and most versatile electric welding process.
Flux-Core (FCAW): Flux-Cored Arc Welding. Like MIG, but the wire has flux inside it. Self-shielded flux-core needs no gas bottle (good for outdoor work). Dual-shielded flux-core uses both flux and external gas for better weld quality.
Short-Circuit Transfer: The most common MIG transfer mode for thin material. The wire touches the puddle and short-circuits, transferring metal in small droplets. Produces a distinctive crackling sound. Lower heat input than spray transfer.
Spray Transfer: A MIG transfer mode where the wire melts into a fine spray of droplets across the arc without touching the puddle. Requires higher voltage and argon-rich gas (usually 90/10 or 95/5). Hotter than short-circuit. Used on thicker material in flat and horizontal positions.
Equipment Terms
Wire Feed Speed (WFS): How fast the MIG wire feeds through the gun, measured in inches per minute (IPM). Higher wire speed means more filler metal and more amperage. Typical range for hobby welding: 150-400 IPM.
Voltage: The electrical pressure that maintains the arc. On MIG machines, voltage controls arc length. Higher voltage gives a wider, flatter bead. Lower voltage gives a narrower, more convex bead. Usually adjusted in 0.5-1V increments.
Amperage: The amount of electrical current flowing through the arc. In MIG welding, amperage is primarily controlled by wire feed speed (faster wire = more amps). In stick and TIG, you set amperage directly. More amps means more heat and deeper penetration.
Duty Cycle: How long a welder can run at a given amperage before it needs to cool down. Expressed as a percentage of a 10-minute period. A welder rated “150A at 30% duty cycle” can weld at 150 amps for 3 minutes, then needs 7 minutes to cool. Lower amperage increases duty cycle.
Contact Tip: The small copper tube inside the MIG gun nozzle that the wire passes through. It transfers electrical current to the wire. Contact tips wear out and should be replaced when the hole becomes oblong or the wire feeds erratically.
Nozzle: The outer cone of a MIG gun that directs shielding gas around the arc. Spatter builds up inside and needs to be cleaned regularly. A clogged nozzle disrupts gas flow and causes porosity.
Liner: The tube inside the MIG gun cable that guides the wire from the drive rolls to the contact tip. A kinked or dirty liner causes erratic wire feeding, bird-nesting, and burnback.
Regulator/Flowmeter: Attaches to the gas cylinder and reduces tank pressure (2000+ PSI) to working pressure. The flowmeter shows gas flow rate in cubic feet per hour (CFH). Typical MIG flow rate: 20-25 CFH.
Auto-Darkening Helmet: A welding helmet with an electronic lens that switches from a light state (shade 3-4) to a dark state (shade 9-13) in milliseconds when it detects an arc. Lets you see your workpiece and position your gun before striking the arc.
Joint Types
Butt Joint: Two pieces of metal lined up edge-to-edge in the same plane. The most basic joint geometry. On thicker material, the edges are beveled to allow full penetration.
Tee Joint: One piece stands perpendicular on top of another, forming a “T” shape. The most common joint in structural fabrication. Usually welded with a fillet weld on one or both sides.
Lap Joint: Two pieces overlap each other, like shingles on a roof. Welded along the edge of the top piece. Common in sheet metal and body work.
Corner Joint: Two pieces meet at an angle, forming an “L” or a box corner. Can be welded inside, outside, or both.
Edge Joint: Two pieces stacked parallel with edges aligned. The weld goes along the exposed edges. Used mainly for joining thin sheet metal.
Weld Types and Anatomy
Fillet Weld: A triangular weld deposited in the inside corner of two pieces meeting at an angle (tee joints, lap joints, corner joints). The most common weld type in structural work. Measured by leg length.
Groove Weld: A weld deposited in a groove between two pieces (butt joints). The groove may be V-shaped, U-shaped, or J-shaped, depending on plate thickness and the required penetration. Also called a “butt weld,” though technically that’s informal.
Bead: A single pass of weld metal. A completed weld may contain one bead (single-pass) or many beads stacked and layered (multi-pass).
Root: The bottom of a weld joint, where the two pieces come closest together. Getting full fusion at the root is critical. A root with no penetration will fail under load.
Toe: The point where the weld bead meets the base metal surface. Undercut, overlap, and lack of fusion all show up at the toes.
Face: The exposed surface of a finished weld. What you see when you look at it.
Leg: On a fillet weld, the distance from the root to the toe on each side. A “1/4-inch fillet” has 1/4-inch legs. Spec drawings call out minimum leg sizes.
Throat: The shortest distance from the root to the face of a fillet weld. The throat determines the weld’s effective cross-section and its load-carrying capacity. On a standard fillet, the throat is about 0.707 times the leg length.
Weld Defects
Porosity: Gas pockets trapped in the solidified weld metal. Looks like tiny holes on the surface or inside the bead. Caused by contamination, inadequate shielding gas, or moisture on the base metal.
Undercut: A groove melted into the base metal along the toe of the weld that isn’t filled by weld metal. Makes the joint thinner at that point. Caused by too much heat, wrong angle, or excessive travel speed.
Lack of Fusion (Cold Lap): The weld metal doesn’t melt into the base metal properly. The bead sits on the surface without bonding. Caused by insufficient heat, wrong angle, or contaminated surfaces.
Burn-Through: The arc melts completely through the base metal, leaving a hole. Common on thin material or when heat input is too high. Fix by reducing amperage/wire speed, increasing travel speed, or using a backing bar.
Spatter: Small droplets of molten metal that spray out from the weld zone and stick to surrounding surfaces. Some spatter is normal in short-circuit MIG. Excessive spatter indicates voltage too low, stickout too long, or contaminated metal.
Slag Inclusion: Pieces of slag trapped inside the weld metal. Occurs in stick and flux-core welding when slag isn’t fully removed between passes. Shows up as dark spots on X-ray or as weak points that crack under stress.
Crater Crack: A small crack that forms at the end of a weld bead where the arc was terminated. The crater (depression at the end) cools and contracts too fast. Prevented by filling the crater: pause briefly at the end of the bead, or reverse direction slightly before breaking the arc.
Positions and Specifications
Welding Positions: Defined by numbers and letters. 1 = flat, 2 = horizontal, 3 = vertical, 4 = overhead. G = groove weld, F = fillet weld. So 1G is a flat groove weld, 3F is a vertical fillet weld, and 4G is an overhead groove weld. Flat is easiest. Overhead is hardest.
WPS (Welding Procedure Specification): A document that spells out exactly how a weld should be made: process, filler metal, current, voltage, preheat, interpass temperature, travel speed, and technique. Required for code work. Not something hobbyists usually deal with, but good to know the term.
Preheat: Heating the base metal before welding to slow the cooling rate. Reduces the risk of cracking in thick sections, high-carbon steels, and dissimilar metals. Common preheat temperatures range from 200 to 400 degrees F (93 to 204 degrees C). Not usually necessary for thin mild steel.
Safety Terms
Arc Flash (Flash Burn): Eye injury caused by UV radiation from a welding arc. Feels like sand or grit under the eyelids, typically showing up 4-8 hours after exposure. Even a few seconds of unprotected exposure can cause it. Always wear a proper shade lens.
PPE (Personal Protective Equipment): Everything you wear to protect yourself: helmet, gloves, jacket, boots, safety glasses, hearing protection, and respiratory protection when needed.
HAZ (Heat-Affected Zone): The area of base metal next to the weld that got hot enough to change its microstructure but didn’t melt. The HAZ can be harder or softer than the original metal, depending on the material and cooling rate. On mild steel, the HAZ isn’t usually a concern. On high-carbon or alloy steels, it can become brittle.
Fume Plume: The visible cloud of smoke and particulates that rises from the weld zone. Contains metal oxides and, depending on the base metal coating, potentially hazardous substances. Always weld in a ventilated area or use a fume extractor. Galvanized steel fumes are particularly dangerous (zinc oxide can cause metal fume fever).
Putting It All Together
These terms are the building blocks for every welding conversation you’ll have. When a forum post says “I’m getting porosity on my 2F fillet, running .035 ER70S-6 at 22V and 350 IPM with 75/25,” you now know they’re talking about a horizontal tee joint weld with gas pockets, and you can start diagnosing whether their voltage is too high or their gas coverage is inadequate.
Don’t try to memorize all 40 terms in one sitting. Bookmark this page and come back when you hit a word you don’t recognize. The terms will stick naturally as you practice.
For cost planning, continue to how much does it cost to start welding. For deeper definitions and technical context on any of these terms, visit the full welding glossary.