Mech was a blanket term for any type of unit the purpose of which was to serve as the backbone of a military ground strike. While the name "mech" itself implies a mechanical origin, the so-called mech-class could in fact refer to anything from trained animals to top-notch machines. The ermegence of mech units coincided wit the development of stronger anti-infantry measures, such as heavy weapons.
Mechs were either wheel vehicles, tanks, modified domesticated animals or robotic walkers that tried to imitate animals, mainly developed by the late Republic and later by the Galactic Empire. Mechs were both assault units and transports of infantry.