Soft loose clothes worn when you definitely wont be leaving the house, worn for warmth and comfort usually over pyjamas. A jogging suit that has never or will never be jogged in.
The act of getting into ones snugglesuit is known as "snuggling up"
" Fuck the pub its pissin down, its my snugglesuit and that big bag of sticky green till the bastard sun comes back out"
"work can suck my balls, im gettin snuggled up and watchin ghostbusters 1 and 2"