A very general term usually referring to or meaning: To steal/tattle on/lurk/creep on/fail/vomit/et cetera.
Again, this term is very universal and can be used for or applied to more than just the above.
Person M: Oh, the usual?
Person K: Daaamn that Stats test was hard!
Person M: Yeah dude, I totally narked it.
Person L: ZOMGZ I TOTZ GOT 110%!
Persons K & M: Stfu.
Person #2: "Maybe you shouldn't tell your friends things that you are trying to hide, dipshit."