noun
number of elements
Technical term used in computing and mathematics, especially for arrays, matrices, or data structures.
この配列の要素数は10です。
The number of elements in this array is 10.
行列の要素数を確認してください。
Please check the number of elements in the matrix.
数 is a general word for 'number', whereas 要素数 is a technical compound meaning 'number of elements'.
Compound of 要素 (element) and 数 (number). A straightforward technical term.