oh, man.... i so liked the idea that it was slang for sex....
Ummagumma - Wikipedia, the free encyclopedia
"The album's title supposedly comes from Cambridge slang for sex, commonly used by Pink Floyd friend and occasional roadie, Ian "Emo" Moore, who would say "I'm going back to the house for some ummagumma".[4] However, some band members have since stated that the word was "totally made up and means nothing at all"."