Cookies are a sweet treat.

Meaning: Cookies are something sweet that you can eat to enjoy yourself.

Choice of Words: Cookies are sweet, round, flat cakes that are often eaten as a snack. Are is a form of the verb "to be" used to indicate the state or condition of something. A is used before a singular noun to indicate one of a kind. Sweet means having a pleasant taste. Treat is something that is done or given to someone as a special pleasure.