Cats chirp to communicate with other cats. Chirps are often used to greet other cats, to start a play session, or to show submission.
Cats chirp to express their emotions. Chirps can be used to express happiness, excitement, fear, or anger.
Cats chirp to get attention. If a cat chirps at you, they are essentially saying "I'm here" and "I want to interact with you."
Cats chirp to ask for food. If a cat chirps at you while you are eating, they are likely trying to tell you that they are hungry.
Cats chirp to initiate play. If a cat chirps at you while they are running around or chasing a toy, they are trying to get you to join in the fun.
Cats chirp to greet other cats or humans. If you come home from work and your cat chirps at you, they are basically saying "hello" and "I'm glad you're home."
Cats chirp to bond with other cats and humans. When a cat chirps at you, they are essentially saying "I love you" and "I want to be close to you."