When you are paid in a form other than cash unexpectedly. This may or may not be something desirable. Term comes from the Trident Layers commercial where the baby sitter is paid in gum instead of cash.
Anyone who pays in gum is extremely cheap.
"I was paid in gum for moving Steve's shit out of his apartment; I got two of his Xbox games."
"Alas poor Yoric, you paid in gum you cheap bastard."
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