Leftover waste or scraps or material deemed useless or disposable.
(attributive, informal) Worthless.
reworded the offal sense inherited from Webster 1913 as "food waste".
added a sense: "something or someone worthless." intended to absorb the attributive sense "worthless" above.
added a sense: Any worthless material, which is intended to absorb the first sense above.
The "space debris" sense seems already included in one or more of the other senses and not to be inherent in the word out of context.
My objection to having an attributive sense for one, but not all, of the senses is that it can be taken as implying that all attributive use of the word has the meaning "worthless". At an abattoir, "garbage collection" handles food waste, in a computer it would handle recovery of formerly used and now unused memory, etc. IOW, almost any noun sense has an associated attributive use. DCDuringTALK 17:38, 26 July 2010 (UTC)