The years from 1990 to 1999, or the decade of a person's life when they are between 90 and 99 years old.
From 'ninety' (Old English 'nigon' nine + '-ty' suffix for tens). The ordinal form 'nineties' has been used since the 1600s.
The 1990s were the last decade before the internet completely transformed culture, which makes it simultaneously nostalgic and archaic—some people call it 'the last analog decade,' even though it had early computers.
Complete word intelligence in one call. Free tier — 50 lookups/day.