In the NYT Magazine on the 6th, a “Who Made This?” piece by Pagan Kennedy on movie popcorn, with this accompanying note on a metaphor:
The industry term for unpopped kernels: spinsters
One commenter disputed this claim, saying that the correct term was old maids. Other sources:
What I do not care for is all those unpopped kernels at the bottom of the bag. Incidentally, these kernels are referred to as “spinsters” among popcorn aficionados. (link)
Unpopped popcorn kernels have been dubbed “old maids” in popular slang, since just as unmarried women that never had children, they do not “pop”. (link)
Apparently there are alternative usages.
From NOAD2 on spinster (originally ‘a woman who spins’):
an unmarried woman, typically an older woman beyond the usual age for marriage.
The word has a derogatory tone that goes beyond an unmarried woman. NOAD2 treats old maid as explicitly derogatory:
derogatory a single woman regarded as too old for marriage.
