If something is scary, it makes you afraid, or scared. Horror films — scary movies — are a very popular genre. Apparently people like to be frightened.

Scary is more a more casual way to say "frightening," and you can also use it to describe something that's just bizarre or odd or exceptional: you've become such a good golfer, it's scary; or, you cleaned up you room so fast, it's scary. Note that there is no "e" in scary, even though the verb to scare ends in one.

Definitions of scary

adj provoking fear terror

“a scary movie”
chilling, scarey, shivery, shuddery
frightening because of an awareness of danger