An
Americanization of the word "
mecha", which is itself a
Japanese-ification of the word "
mechanical". A
mech, or
'mech, or
mecha is basically the same thing as a
giant robot, with the exception that a
mech is almost always
piloted. In other words, it is a large
mechanical vehicle of (sometimes very
vaguely)
humanoid form.
Besides the examples Hai-Etlik gives, I would point out that Macross, Neon Genesis Evangelion, The Vision of Escaflowne, and Gunbuster, among many others, also feature mecha.