It is urban slang. It means to leave a place where there are a number of people to go someplace alone and pass wind (fart) in order to avoid embarrassment. "Boy, that curry I ate for lunch is starting to attack. I need a beef walk - I'll be back in a minute." It is very seldom used. In fact, many English speakers do not know the definition - it is purely American and many Americans don't know it.

Australians never use this expression. Most say: Excuse me, I'll be back in a minute.