Gundam is a large (50-60 foot I think) Robot that was made becuase Minovsky particles made it so you couldn't use radar. (bad reason)
It was a Japanese cartoon that aired from 1979 to 1980.
Basically it was so succesfull everyone who watched wanted to have a gundam of their own so they made models.
Edit: Sorry, I'm used to having a small font size on another site. 