Definition of "mecha"

Having deprived her of both her mecha and her lover, Masato looks set for a nasty end, but Miku arrives to save him.

1997, Helen McCarthy, The anime movie guide

A transformation occurs when a mecha character, vehicle, or weapon unfolds and reassembles itself in a totally new form.

2002, Christopher Hart, Anime mania: how to draw characters for Japanese animation

Porco Rosso evinces a deep fascination with mechanical objects of all sorts but it is by no means a mecha movie...

2006, Dani Cavallaro, The animé art of Hayao Miyazaki

Each week the good guys fight the bad guys and vanquish them in a mecha battle, only to have the bad guys reappear intact the following week.

2007, Frenchy Lunning, Mechademia 2: Networks of Desire

[…] to be a “lifter”—to pilot a mecha that can also transform into an air board […]

2007, Robin E. Brenner, Understanding manga and anime, page 170

In this section, I show you mechas that are large enough to be piloted by humans from the inside. Although most of them are designed for combat, some function as transportation or construction mechas.

2011, Kensuke Okabayashi, Manga For Dummies, page 275