When designing a welded joint, there are minimum mechanical strength requirements that must be met.
A weld procedure defines stuff like joint perparation, weld filler metal to be used, voltage or current settings, shield gas, pre-heat, position, number of passes and speed...
Sample joints are then made and destructively tested to demonstrate that a weld produced to that procedure will produce the required joint strength. This qualifies the procedure.
Then, individual welders must demonstrate that they can produce that weld. Welder qualification.