LW

Stands for Lettuce Wedge, according to YouTube legend LWsquidward, which is a person on YouTube who is a legend.

Magoo: "What does the LW in LWsquidward mean?"
Wise Nobleman: "Lettuce Wedge"
Magoo: "uh ok m8 what does that mean lol rofl lmao imo"
Wise Nobleman: "It means an object being broken down with lettuce from the inside"