Arduino motor shield

Hi! I am completely new in this area (but old anyway :. ). Due to this I am not shure what is the meaning of the word "shield" in "Arduino motor shield". Is it separate PCB with diferent components on it and with purpose to isolate and protect Arduino board from high electrical load? Thank you for the answer.

http://arduino.cc/en/Main/ArduinoShields "Shields are boards that can be plugged on top of the Arduino PCB extending its capabilities. The different shields follow the same philosophy as the original toolkit: they are easy to mount, and cheap to produce."