Official Aviation Definition
The Touchdown Zone (TDZ) is the first portion of a runway beyond the landing threshold, typically extending 3,000 feet (900 meters) down the pavement or the first third of the runway length. It is designated by painted longitudinal rectangular markings and white TDZ centerline lights.
In Simple Words
The target landing zone marked with white painted stripes on the runway where planes aim to put their wheels down.
Real-World Flight Example
The captain touched down smoothly in the center of the touchdown zone 1,200 feet past the runway threshold.