GUMPS is an acronym used in fixed-wing aviation - at least, I know it's used in general aviation. It is a quick way to remember a checklist to be used when in the traffic pattern for landing and before beginning descent. It stands for:
- Gas - is the fuel selector valve set properly? ('ON' or 'BOTH' depending whether your airplane has multiple tanks)
- Undercarriage - landing gear. If your airplane has retractable landing gear, is it down? Apparently there are an average of 100 'gear up landings' each year in the U.S. because yes, sometimes pilots forget.
- Mixture - fuel/air mixture. Is it set properly, to fully rich (you lean your mixture at higher altitudes, so this ensures you remembered to enrich it after your descent to the airport).
- Propeller - make sure your prop is set correctly for landing, according to your aircraft manual. For example, the Cessna 182 Skylane should have its prop set to HIGH RPM (fine pitch).
- Seatbelts and switches - check that all passengers have seat belts and shoulder harnesses, as required, properly secured. Make sure any switch settings that need to be done are done - for example, ensure your strobe and landing lights are turned ON and your autopilot turned OFF.
Although it sounds like a set of obvious things, they're all very important - and landing, especially at the end of a trip and descent, can be a time of high pilot workload especially if he or she is at an unfamiliar airport. A great deal of time is spent looking outside the airplane, making sure it is in the right configuration relative to the ground, which is occupying a great deal of the pilot's attention (and properly so) at this point. This quick check ensures that the critical tasks that should be done before beginning the final descent to land are, in fact, complete.
If your airplane is not a complex airplane, then you won't have undercarriage or propeller settings to worry about and of course you should just skip those. But better to go over the whole list and decide consciously 'nope, I don't need that' than not bother to check.
GUMPS. Remember it.