Snuck is the past tense of sneak, meaning to move quietly and secretly to avoid being noticed or caught. When you snuck downstairs on Christmas morning to peek at presents, you tried to stay silent and out of sight. When someone snuck into the movie theater without paying, they slipped past the ticket taker hoping no one would see.

The word suggests deliberate stealth and secrecy. You might sneak (or have snuck) extra cookies from the jar, snuck a note to your friend during class, or snuck up behind someone to surprise them. Animals also sneak: a cat snuck up on a bird, moving carefully so its prey wouldn't notice.

Some people prefer “sneaked” as the past tense, and both forms are correct, though snuck has become increasingly common in everyday speech. Whether you write that you snuck or sneaked out of a boring assembly, everyone will understand you moved quietly, hoping no one would notice you leaving.