What is a portmanteau?

This is a good start on this forum as it is about language. Today when surfing the web for avatars, I stumbled upon a neat page that has introductions about several manga and anime. In particular in reference to portmanteau was the anime introduction about Azumanga Daioh.

There's a wikipeida on Azumanga Daioh and it is here where the word portmanteau is used.

Check it out, folks!