From Traderpedia

Used to voice an opinion in the belief that a market or some aspect of it is going to rise.

This is the opposite of being bearish.

A Bullish market is one where prices increase over a long period of time. It happened during 1982 - 1987 and again in 1995 - 1999. Bull markets occur when around 80% of all the stocks increase steading over a period of time.