The other definitions have the right meaning (a sloppy kiss where you blow, making a farting sound,) but this spelling and pronunciation have diverged from the original, and should be considered incorrect.
This word was first introduced on "The Cosby Show", (Season 2, Episode 11) and explicitly spelled out "ZRBTT
". It was also clearly pronounced without the final "r" sound given here. It was spelled repeatedly by several characters. The subtitles as aired on the show spelled it "Zurbitt" when Bill Cosby was pronouncing it as if it were a real word. Part of the joke of this word is that it's a nonsense spelling without vowels.
In the episode, Vanessa was practicing for a spelling test, and Rudy kept interrupting, asking what a series of nonsense letters spelled. The following, including spelling, is taken from the subtitles as transmitted.