Chumma means "Kiss". It is an extremely common word used in India, where I believe the word originated, just like "maya", "pandit" etc. My definition below is for the Indian word "chumma".
When using it as a "goodbye", care MUST be taken to use towards the opposite sex ONLY. The chumma in "see ya later.. chumma" means "kisses".. it DOES NOT mean "goodbye". Unless you are a homosexual or want to come out as a total ignorant, never use it against the same sex.
Having said that, it is actually used most often in sentences like "see ya later.. chumma" or "see you tomorrow.. bye and chumma". Again, if you want to add chumma to your sentence, it has to be towards the opposite sex. It generally does not mean "kiss" in a serious way and so its highly unlikely the girl will get offended when a guy uses it on her. Its also very commonly used amoungst friends.
Since another person here have said the word means "goodbye", I want to re-assert the Indian word "chumma" means KISS... MAKE NO MISTAKE on that. I have come across some foreigners use it incorrectly, but "goodbye" is not what it means.
ONLY TOWARDS THE OPPOSITE SEX: "see ya later.. chumma"
Boy asking girl: "can I have a chumma"
Speaking to a baby: "Give mommy/daddy a chumma"