In science fiction, mecha (Japanese: メカ, Hepburn: meka) or mechs are giant robots or machines, typically depicted as piloted, humanoid walking vehicles. The term was first used in Japanese after shortening the English loanword 'mechanism' (メカニズム, mekanizumu) or 'mechanical' (メカニカル, mekanikaru), but the meaning in Japanese is more inclusive, and 'robot' (ロボット, robotto) or 'giant robot' is the narrower term.
Fictional mecha vary greatly in size and shape, but are distinguished from vehicles by their biomorphic appearance, and are often much larger than human beings. Different subgenres exist, with varying connotations of realism. The concept of Super Robot and Real Robot are two such examples found in Japanese anime and manga.
Real-world piloted humanoid or non-humanoid robotic platforms, existing or planned, may also be called "mecha". In Japanese, "mecha" may refer to mobile machinery or vehicles (including aircraft) in general, piloted or otherwise.