Giant robots used by the Power Rangers able to combine into a bigger one, often called a "Megazord". They can represent various things, usually animals or vehicles. Each Ranger can drive one single Zord.
Zords are named after Zordon, the mentor of the original Power Rangers.
In the Super Sentai series (the japanese series which Power Rangers is based on), the Zords are not called as such, they are simply "mecha". That said, the collective name varies between series. For example, in Zyuranger they are the Shugojuu, whilst in Go-onger they are the Engines.