Definition & Meaning of "narc"in English

What does "narc" mean in law enforcement and street slang?

The structure is a clipped shortening of "narcotics officer," dropping the final syllables to create a quicker, more casual noun. It is used to describe a police officer or federal agent working on illegal narcotics control, often one who investigates, arrests, or infiltrates drug operations. People typically use "narc" as a neutral descriptor in news or police contexts, but in street slang it carries a negative or fearful tone, as in "Watch out, that guy's a narc."