Can be used in a variety of contexts, most often to express dissatisfaction, or that you think whatever you're talking about is silly or stupid. Can also be used mid-sentence, for example "I gammon told her that she is a frog" or "I was just gammoning!" indicate that what was said, was said in a joking manner. In wide use in the Northern Territory of Australia.
Definitions include: to send a parolee back to prison for up to one year -- without trial, on the recommendation of his parole officer or the Board of Prison Terms "Parole Board"), but any such time spent incarcerated is still wearing down his remaining parole (parole is most often 3 or 4 years, starting from the date on which the parolee is initially released from prison, after which he is 'discharged').