Bear market
What does it mean to say a market is in a bear market, and how is that different from one bad week?
In plain words
A bear market is a long decline from a peak, commonly described as a fall of roughly a fifth or more, though deeper and longer falls are typical. It describes the whole arc of falling prices over months, not any single day or week.
Why it matters
A market deep below its previous high behaves differently from one near it: rallies occur inside it and can be large, and losses compound over a long period. Reading a single week's decline in the context of the distance from the peak changes what that week means.
In a real week: ETH, week of 8 April 2019
In the week starting 2019-04-08, ETH opened at 174.29 and closed at 167.23, a weekly return of -4.05%, and it was 80.08% below its 52-week high — far past the fifth-or-more threshold. Yet the prior four weeks included three up and one down, with one up 23.19%. Volume was 1.52 times its prior 12-week average, and the weekly return sat at the 40th percentile of the 60 weeks of history.
A common mistake
Treating one sharply down week as the definition, or assuming every week inside a bear market falls. Rises and mixed stretches are normal within a longer decline.