No cap usually refers to the phrase "no lie"

A word used by Graffiti writers, ;to be capped out

-when one writer goes over or marks a line threw any other writer..

Caps lock on a computer keyboard. Represents SHOUTING in chat rooms,IRC chats and forums...

means that you’re not lying and are being serious. originated from the twitch emote Kapp and non twitch users started using it as “Cap” after hearing twitch users started saying it in public.

Term used for the cap of a mushroom, usually one of the psychedelic nature.

refers to the ignition cap at the base of a cartridge for a firearm. "bust a cap" means break the cap by pulling the trigger, setting off the explosion that propels the bullet

A person,who always tells such obvious things that people around think he is really stupid.
Caps are usually ridiculed.