When someone's playing trackmania and takes a jump in a rough way which causes the car to flip a bit when it lands, it's considered a landing bug.
a: dude, you totally need to improve your skills.
b: my skills are fine. it was just a landing bug.
a: oh ok. it looked as if it was your own fault first.
A thing in "TrackMania Nations Forever" which is triggered by landing on the ram at a weird angle causing you to lose speed. It is also the cause of the hate of dirt roads because the entire road is prone to landing bugs.