What is a landing burn?
Also called: hoverslam, suicide burn
The landing burn is the final engine firing that brings a booster from fast to stopped, right at the ground. It is also called a hoverslam, because the rocket cannot hover.
By this point the booster is nearly empty and therefore light. Even throttled all the way down, a single engine still pushes harder than the empty booster weighs — so lighting it does not slow the rocket to a hover. It slows, stops, and starts climbing again.
The burn therefore has to be timed so that speed and height reach zero at the same instant. There is no hovering to correct a mistake and no second attempt.
On a Falcon 9 it starts around T+7:52 and touchdown is at about T+8:15.
See it happen
Coming HomeLanding on its feetSource: Falcon 9 Block 5 mission timeline (Starlink Group 17-38)