Glossary Entry: Sentient

A creature (or other entity) is considered sentient if it capable of both understanding its environment and acting upon this understanding. You are sentient, for example, as is your pet cat and other animals, but your houseplants are not.

In fiction, this term often gets confused with sapient. Sapient entities are effectively equal with humans when it comes to reasoning and intelligence; ie, a sapient creature is basically a "person" with all of the rights that entails.