Flare

Flaring refers to raising the aircraft's nose in the last stage of landing, in order to arrest the rate of descent. This is also called a roundout by some.

Since the usual rate of descent on the approach to a landing is faster than the aircraft is designed to take on touchdown (not to mention occupant discomfort), that rate of descent must be slowed to almost nothing just before touchdown (except in a carrier landing -- another story entirely), in order to prevent damage to the aircraft and even potential loss of control at touchdown.

So the nose is smoothly raised just before touchdown (sometimes power is also added) to almost stop the descent, in order to allow a gentle touchdown.