Nasty fat in some meat, wads or cartelidge.
Called spu-lunk-a-gunk because it's 'like eating the crap in a cave that tastes like when you eat chicken' A.K.A really nasty. see ga boing ga
'Ew, sick, this chicken is full of spu-lunk-a-gunk, omg, I'd rather lick bat crap off the bottom of a cave!'
'Dude, it's the same thing...'