A chub is an overweight or obese gay man who identifies as being part of the chubby culture.
There is also an annual event in Europe called European Big Men's Convergence.
Of note, the term chubby chaser can also be found in use among heterosexuals, most commonly referring to a man (usually thinner) who is sexually attracted to heavier, overweight, or obese women.
[1] While casual social networks for chubby men and chasers had long existed, the first organized social group in the United States, Girth & Mirth, formed in 1976 in San Francisco.
Formally organized Convergence conventions in the United States were first held in Seattle in 1986.