Basic Trope: A character is transported in the trunk of a car.
Straight: Alice is placed in Bob's trunk.
Alice's mouth has been taped shut, and her hands and feet are taped behind her.
Alice is dead.
Alice, along with 10 other people, are placed in Bob's trunk.
Downplayed: Alice is in the trunk, but it's one of those trunks that's contiguous with the main interior of the car, so she's got plenty of air and could easily get out just by climbing over the back seat.
Bob is carrying Alice off as a hostage.
Bob has murdered Alice, and is transporting her body to dispose of it.
Alice is a fugitive, and Bob must keep her hidden.
Zig Zagged: Some hostages are transported in the trunk, others in the car itself.
Averted: No people (alive or dead) are found in Bob's trunk.
Enforced: Alice's actress needs a sick day right in the middle of a Road Trip Arc. So Alice goes missing for an episode and is discovered to have accidentally shut herself in the trunk once her actress returns.
Lampshaded: "I'm gonna stuff that bitch in the trunk when I'm through with her!"
Invoked: Bob kidnaps Alice, and needs a way to transport her covertly.
Exploited: Alice knows Bob's first choice is going to be the trunk, and it's all part of her escape plan.
Defied: Bob does not own the car, and instead holds a gun to Alice (the driver's) head, telling her exactly where to go.
Deconstructed: These days, a lot of car manufacturers anticipate this very thing, and so there is usually a way for the person in the trunk to open it from the inside and escape. And if Alice is dead, and Bob leaves her body in there (i.e. forgets about it), then she'll decompose, which will be a hell of a stench to clean up (and try to hide.)
Reconstructed: Bob takes out the safety feature (or simply does not put one in), and either only transports live people this way, or makes sure to take dead bodies out.
Played For Laughs: Bob "kidnaps" his friend Alice from her job to "hold her hostage" someplace more fun.