A sitter is someone who watches and cares for children, pets, or a house while the regular caretaker is away. The most common type is a babysitter, a person (often a teenager or young adult) who stays with children when their parents go out for the evening. A pet sitter might visit your house twice a day to feed your cat and play with your dog while your family is on vacation. A house sitter lives in someone's home while they're traveling, keeping it safe and maintained.

Good sitters are responsible and trustworthy because people depend on them to keep children, animals, or property safe. Parents often hire the same babysitter repeatedly once they find someone reliable whom their kids enjoy spending time with.

In sports, a sitter means something completely different: an extremely easy scoring opportunity that a player surprisingly misses. When a soccer player has an open goal with no defenders nearby but somehow kicks the ball wide, commentators might say they “missed an absolute sitter.” It's called this because the chance was so easy it seemed like you could score it while sitting down.