noun, noun which may take the genitive case particle 'no'
dozens; scores of; decades
Indicates an approximate number from several tens to under a hundred. Used for countable items, people, years, etc. When referring to years, it often means 'decades'.
Dozens of spectators gathered at the venue.
Dozens of spectators gathered.
This town changed greatly decades ago.
The number of victims is believed to reach the dozens.
The discovery was the result of decades of research.
数十 means an approximate number in the tens (twenty‑ish to ninety‑ish, i.e. 'dozens'), while 十数 means just over ten (i.e. 'ten-odd' or 'a dozen or so').
数百 means 'several hundred', while 数十 means 'several tens'—an order of magnitude smaller, so the two are easy to mix up when reading quickly.
several decades; many decades; a few decades
Compound of 数 (すう, 'several') and 十 (じゅう, 'ten'), literally meaning 'several tens'.