In article >, says...
>
> "Ophelia" > wrote in message
> ...
> >
> > What exactly is a chub?
>
> Ground beef sold in a tubular package. No clue why.
>
> http://www.swagbucks.com/?t=i&q=chub+of+ground+beef

Back-formation from chubby.

chub (plural chubs)

1. A chubby, plump person
2. (LGBT slang) An overweight or obese *** man.
3. A plastic or other flexible package of meat, usually ground meat or
luncheon meat.

(https://en.wiktionary.org/wiki/chub)