1. A trader who hopes to make quick profits. Basically, another term for "speculator".

2. A British and Australian term for one who gambles, a bettor.
A punter's approach is to speculate rather than invest. Thus, punters aren't concerned with the fundamentals of an investment; instead, they attempt to make a quick profit by selling to somebody else at a higher price. Punters speculate in any market, but especially like options, futures and forex because of the leverage.