In British English, the dessert course served after the main meal; sweet foods eaten at the end of dinner.
Shortened form of 'after-dinner' items, with the -s making it a noun. This informal British term became common in the 20th century.
The word 'afters' is a distinctly British invention because the formal British multi-course meal structure made it natural to refer to the final sweet course as simply 'what comes after'—it's linguistic efficiency.
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