A bull market is generally a rising trend in stock value.
Bitcoin is currently in a bullish market (relative short duration of three months, and likely to retrace)
, and likely to retrace).
A bull attacks by raising its horns upward while a bear attacks by swiping its paws downward, hence the terms bull market (going up) and bear market (going down).
There are no hard and fast rules but if growth has been consistently upward for a few years, then this is a bull market.