When a welder makes a small weld bead to "tack" a joint together so it will not move. This makes it easier to weld a joint without having to clamp it.
Tack welding is when a welder makes a small bead to "tack" the metal into place for the final welding.

350kg

tack

First, Butt-weld is short for a butt groove. Welding in a butt-groove starts at the throat of the butt-groove. The first weld point could be a tack-weld: holding the two materials to be welded together. The throat is measured and filler metal and electrode are determined to create the root pass.

You have to break the tack weld on the lip of the skin that raps around the door fram.