Bull market is commonly described when prices of financial assets such as stocks and crypto currencies are rising. It occurs when direction of market is upwards driven by positive sentiments of investors and traders. On the contrary, the bear market characterized  a period of time when market activity is low, trading volumes are on decline and consequently prices of trade-able assets are falling.
It is important to note that bull and bear cycles are typical behavior of any market which is generally driven by fundamental factors, including overall state of the economy, interest rates, GDP growth and above all political stability.