Bull = rising prices, optimism. Bear = falling prices, pessimism.
Example
In the 2020–2021 bull market, Bitcoin rose from around €5,000 to over €55,000 — rising prices, optimism, every dip bought. In the following 2022 bear market it fell over 70%, marked by fear and capitulation. Sentiment changes which strategies work: in a bull market holding pays off, in a bear market capital preservation is king. Knowing the broader market phase lets you trade with the trend, not against it.