From Monkey Island wiki
Brillig Island is a small island in the Gulf of Melange. It features only a small beach area with some coconuts and a rubber tree. Trenchfoot and Hardtack occasionally visit the island to bury the Seahorse summoning artifact here or to dig it back up.
The word 'brillig' was coined by British Victorian author Lewis Carroll in his nonsense poem "Jabberwocky"; apparently it means "four o'clock in the afternoon, the time when you begin broiling things for dinner". Snark Island is also named for one of Carroll's nonsense words.