Tack Weld
A tack weld is a temporary or integrated small welded joint used to fix the relative position of components prior to the main welding process. It prevents impermissible positional changes caused by thermal distortion.
Tack welds are short weld spots that fix the components in position before you weld the actual seam. If you make them too small or too weak, they will tear during cooling or due to shrinkage of the main weld, and your workpiece will distort. So set them strong enough, but not so large that they interfere with the later seam or are hard to grind off. Make sure the tacks are fully penetrated and free of lack of fusion, otherwise you'll get cracks in the main weld later. Distribute them evenly along the length of the part so nothing shifts during welding.