I often find myself describing what a grip does to people outside the industry and to people inside the industry that don't actually know precisely what we do. Depending on who's asking and how much time I have the answer can vary from one very unspecific and slightly inaccurate word to a multiple part definition that really defines what is grip and what is not. So here is my answer to the question posed and improperly answered in the Naked Gun 2½ credits: "What the hell is a Grip?"
Lighting¹ ² ³
¹ Incomplete: This definition ignores a large part of what we do.
² Incorrect: This definition states that we do the opposite of what we do.
³ Misleading: This definition appears to give us credit for a function that we are only partially responsible for.
Grips are responsible for shaping and controlling light and rigging cameras and lights. ¹ ²
¹Vague: While accurate, without knowledge of the terms used its definition is foggy at best.
²Incomplete: Still ignores a large part of what we do.
Grips shape light by adding shadows, diffusing the light, and bouncing the light. Grips are also responsible for rigging the placement of any light that does not go on a normal light stand. Likewise, any time a camera goes anywhere other than a tripod grips are responsible for rigging or securing it. ¹
¹Incomplete: While getting closer, it still doesn't quite cover all that we do.
The Grip department is part of the lighting department. The other half of the lighting department is the electric department. While the electric department actually provides the light by running power, setting up the lights, and operating the lights; grips role in the art of lighting is refining the raw output of the lights into something that looks like it actually exists in real life and fulfills the Cinematographer's vision for the film. This is accomplished in a number of ways using a wide variety of equipment but the main four modes of shaping light are bouncing, diffusing(softening), netting(reducing the intensity), and cutting(actually shadowing).
We also assist the electric department by making places for them to put lights that can't be on a normal stand. This is generally known as rigging¹ and depending on the location and where the light needs to be placed it could be as simple as using wood screws to attach a plate to a set wall or as complicated as designing a cantilevered crane to support the light.
Likewise, anytime the camera goes anywhere other than a normal tripod we support it. That mainly includes cranes, dollies, steadicam, or even just hand held in which case we operate the equipment that carries the camera. Certain specialty equipment(steadicam, specialized cranes, etc..) comes with a technician or operator that runs the equipment, but even then we assist and support them. Sometimes that includes rigging the camera to things that weren't designed for a camera. Cameras can be rigged to almost anything: cars, planes, animals, body parts, doors, bowling balls; and grips are the ones to come up with a way to make that happen.
The last thing Grips are responsible for is hard to define because it's really the et cetera of filmmaking. If it isn't covered under any other department and grips have the tools to solve the problem then we're probably responsible. This can be anything from making an impromptu changing room for an actress in the middle of the desert to providing a blood splash barrier for the camera operator. The list of things that grips have done in this category is as long and diverse as the movies that they've been done in service of.
¹In this sense the term rigging loosely means "attaching this thing to that thing" but in the industry rigging can also mean the lighting work that's done by a separate crew ahead of time.
My Go-To Definition:
We're the subtractive side of lighting; and anytime a light or camera goes anywhere but a stand or tripod, that's us.
I hope that helps you get a better idea of what a grip is. Feel free to comment below or send me any questions here.