slang contraction of is not, are not, am not, do not or does not.

lil mad is like big mad but the opposite, you mad but not mad to the extent of pullin somthin

informal language;teachers hate it;used in texting,talking

Short for "am not" and for nothing else – not even "is not", for "it ain't" would just be "it am not". The only correct use is "I ain't" which is a contraction of "I am not". So, don't say e.g. "you ain't" which would only mean "you am not".

<negative third person singular> Chiefly American Colloquial Contraction

A single word that is equivalent to other words such as:
1) Am not
2) Are not
3) Is not

==> Most likely originated in the Southern States of America as it flows easily with their accent but has now been used in many places around the world.

Is now in a dictionary