파 is a suffix meaning faction because gangsters are usually in certain group so we call them xx파 usually it is used in other fields even daily life.

It is probably the best suffix to use to describe them. -파 means a loosely associated people who share some characteristics or who follow the same cause or trend. It is very broadly used for both good and bad groups of people (e.g. 인상파 = The Impressionists). There is -단 which is for more closely organized groups (for good or bad cause), and -패 (as in 깡패) for smaller and more informal groups. -파 sits between these and can describe the loose organization of gangs better. Actually, those labeled as XX-파 are usually bigger than what you may call 깡패(들). They are often called 조폭 (short for 조직폭력배 = organized thugs). 깡패 is a term for small time, not so organized street thugs.