No, a best boy is not a groom's right hand pre-teen in a wedding party. At least, not on a film crew, where they actually act as assistants to department heads, like the gaffer and the key grip.

Think of it this way: if the gaffer and the key grip are the owner of the store, the best boy is the manager. She (yes, despite the title, they aren't always boys) or he is responsible for everything from hiring to scheduling crew to renting equipment and workplace safety. What else do they do? We'll let Film 101 host Amanda Parris take things from here...