1A prefix meaning several / a few / a number of; indicates an approximate quantity.
数人が会議室に集まった。
A few people gathered in the conference room.
数回練習すればできるようになるよ。
If you practice a few times, you'll be able to do it.
数万円の出費がかかる見込みだ。
It's expected to cost several ten-thousands of yen.
2Number; quantity; amount — the count or amount of something. Most often appears as the second element of a compound (e.g., 人数, 部数, 総数).
参加人数を事前に把握しておく。
We make sure to know the number of participants in advance.
出版部数が予想以上に伸びた。
The number of copies published grew more than expected.
在庫の総数を確認してから出荷する。
We check the total inventory count before shipping.
3Counting / calculation; figures or numerical values used in calculations or statistics — often appears in academic or formal phrasing like 数の概念 (the concept of number).
数の概念は算数教育の基礎になる。
The concept of number is fundamental to arithmetic education.
統計上の数を正確に把握する必要がある。
It's necessary to accurately grasp the statistical figures.
4A number; a numeral or figure — the concept of a numeral in grammar/mathematics.
数学では自然数や整数といった数の種類がある。
In mathematics there are types of numbers like natural numbers and integers.
ゼロは特別な数として扱われることがある。
Zero is sometimes treated as a special number.
5Grammatical number (e.g., singular vs. plural).
この言語は名詞に数の区別がない。
This language has no grammatical number distinction on nouns.
ラテン語では名詞の数が形に現れる。
In Latin, the number of a noun appears in its form.
6Fate or destiny; the course of events (literary/archaic). Rare as a standalone word in modern Japanese — mostly seen in compounds like 天数/運数 or in proverbial expressions.
「事の成るも成らぬも数だ」と老将軍は静かに言った。
'Whether things succeed or fail is fate,' the old general said quietly.