What is an entry burn?
An entry burn is a short engine firing that a returning booster makes into the oncoming air. It slows the booster, but its main job is to shield it from re-entry heating.
Coming down, a booster runs into thickening air that cannot get out of the way fast enough. Compressed air gets extremely hot, and that is what destroys most returning spacecraft.
Firing three engines into the airflow pushes a cushion of the rocket’s own exhaust ahead of it, so the worst of the heating happens in the exhaust rather than on the vehicle.
On a Falcon 9 the entry burn runs from about T+6:09 to T+6:30.
See it happen
Coming HomeLanding on its feetSource: Falcon 9 Block 5 mission timeline (Starlink Group 17-38)