Official Aviation Definition
Final approach is the terminal flight path segment in the direction of landing, aligned with the extended runway centerline. It extends from the final approach fix (FAF) or pattern turn down to touchdown on the runway threshold.
In Simple Words
The straight-in descent path where the airplane is lined up directly with the runway just before touching down.
Real-World Flight Example
On 3-mile final approach, the captain confirmed the aircraft was fully stabilized with green landing gear lights and landing flaps set.