An unattractive, old fashioned and often huge style of underpants/breifs, worn by pensioners and people with appalling fashion sense.
Often spotted covering large asses, where the lining of the granderpants are visible through pants/jeans and exposed to the unfortunate public. Also commonly spotted on people with grotesque and fat behinds.
As Jim walked down the street he noticed a fat old lady wearing a gross flowery dress with her huge pantie line clearly visible underneath. A gust of wind blew up her dress further exposing her brown huge underwear, that was struggling to contain her huge, fat and saggy ass. It was then Jim knew he had spotted a pair of granderpants.