Falcon 9 first-stage landing tests
The Falcon 9 first-stage landing tests were a series of controlled-descent flight tests conducted by SpaceX between 2013 and 2016. Since 2017, the first stage of Falcon 9 rockets are routinely landed if the performance requirements of the launch allow.
Source: Wikipedia — Falcon 9 first-stage landing tests (CC BY-SA 4.0)