From Wikipedia
Planetfall is a science fiction interactive fiction computer game written by Steve Meretzky, and the eighth title published by Infocom in 1983. Like most Infocom games, thanks to the portable Z-machine, it was released for several platforms simultaneously. The original release included versions for the PC (both as a booter and for DOS) and Apple II. The Atari ST and Commodore 64 versions were released in 1985. A version for CP/M was also released. Although Planetfall was Meretzky's first title, it proved one of his most popular works and a best-seller for Infocom; it was one of five top-selling titles to be re-released in Solid Gold versions including in-game hints. Planetfall utilizes the Z-machine originally developed for the Zork franchise and was added as a bonus to the "Zork Anthology".
The word planetfall is a portmanteau of planet and landfall, and occasionally used in science fiction to that effect.