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'.
数十人の観客が集まった。
Dozens of spectators gathered.
Dozens of spectators gathered at the venue.
この町は数十年前に大きく変わった。
This town changed greatly decades ago.
被害者の数は数十にのぼるとみられている。
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'.