noun
Refers to how many there are: a count, quantity, or numerical amount. Common in patterns such as 数が多い, 数が少ない, and 数を数える.
参加者の数が増えている。
The number of participants is increasing.
箱の中のりんごの数を数えた。
I counted the number of apples in the box.
数字 refers to a numeral or digit as a written symbol, while 数 refers more broadly to a number or amount.
番号 is an assigned identifying number, such as a phone number or ticket number; 数 is simply a count or quantity.
数量 is a more formal word for quantity or amount, especially in counting, statistics, business, or technical contexts.
数 is the conventional kanji spelling for the native Japanese reading かず, meaning a number or count. The exact historical derivation of かず is not specified.