A little of the same but in a heirachy. Key Grip is the top of the people who move lighting stands, cables, stingers, and rigging so that the lighting and electrical departments have all of the power and sources they need to light a set. The Best Boy is the next position below the Key grip who does the same, but more manual. Smaller movies, for example, won't have a best boy... just a Key Grip, and then a team of "grips"