A gumball is a ball of gum that first appears in the episode "The Paper."
They are hard, small, and spherical balls of gum that come in many different flavors and colors.
Role in the series
It appears when Squidward lays down in the sun and bites it into regular gum. The wrapper it comes in also becomes a vital aspect of the episode, as he litters it onto SpongeBob's front lawn, who uses it as an entertainment source named Mr. Paper.