The Bear Flag is, as its name suggests, a bearish continuation pattern. Bear Flags generally evolve after a period of pullback followed by some sideways consolidation.  They are so named as the decline appears like a Flag pole and the the consolidation phase appears like a Flag.

The Bear Flag example arose during the market pullback on the ASX-200 index during March 2020:

ASX-200 4hr: The ASX-2000 pulled back from the 7,200 High region and then consolidated around the 6,400 level:

ASX-200 4hr: The index started to breakdown from this Flag style consolidation where the Flag pole was a round 1,000 points. This image was Tweeted out on March 6th:

ASX-200 4hr: The index delivered a fall of 1,000 points by March 10th thereby completing this Bear Fag breakout pattern. Note how price action reacted at the 10 year support trend line; this was always going to be a good place to take profit:

Summary: the Bear Flag is a bearish continuation pattern. They are worthwhile patterns to try and identify across charts as they have a better than a coin toss probability of some decent follow-through, even if not for the whole of the projected target. It is useful to use a momentum indicator in conjunction with the trend line breakout to give confidence there is momentum for any breakout move.