Gummy is a giant ball of chewed gum that consists of a moldy slice of pizza, a pair of underwear, dirty socks, a used toothbrush, saliva, and other disgusting items.
Role in series
"The Gift of Gum"
It is one of Patrick's greatest possessions. He gives it to SpongeBob on Best Friends Day. SpongeBob is disgusted by Gummy. Eight fish even lived in it (which Patrick seemed unaware of), but SpongeBob eventually frees them.
SpongeBob hates Gummy so much that he tries to dispose of it in any way he could, which includes burying it and dumping it in a trash can. Later, SpongeBob, Sandy, and Squidward all are stuck in Gummy. When SpongeBob gives it back to Patrick, he eats it, but then winds up burping it out as a result of the hiccups he receives from consuming it. This leaves Bikini Bottom covered entirely in gum.
SpongeBob's Truth or Square
Gummy helps get SpongeBob across in some levels.
When cleaning the gum off the bottom of the tables in the Krusty Krab, SpongeBob puts all of the gum into a giant ball and says that he will give it to Patrick after work.
There used to be a living pair of ripped underpants inside of Gummy that knew who Patrick was.
According to SpongeBob's Director's Commentary for the level "Hide And Sneak!," Patrick uses Gummy to store old socks, bits of food, kelp, and other things. When it reaches critical mass, it transforms into a "giant mass of putrescence."