"Bussi" (das) means (short, non-French) "kiss".
"schlecken" means "to lick", and "schleck" is the Mickey-Mouse-style* shortened form of it.
The word "Bussi" is used primarily in Austria and Bavaria, I have no idea how much it extends northward.
"Bussi" is sometimes also used as a relatively intimate greeting; among close family members, among lovers. It is not considered obscene.
"Bussi schleck" is not a set phrase, but I can perfectly imagine a pair of lovers making it up as a slightly erotic private greeting. The reference to licking makes it slightly obscene; it would be OK for friends of the couple to overhear it, but the couple should not use it in "polite society".
* yes, really: this grammatical form in the German language was essentially made up to translate things like "*sigh*" in Mickey Mouse comics to "*seufz*"); this form is also called "Inflektiv" or "Erikativ" after its inventor, Erika Fuchs.