noun
undefined value
Computing term for a variable or expression that has not been assigned a defined value.
この変数は未定義値のままなので、計算に使えません。
This variable remains an undefined value, so it cannot be used in calculations.
未定義値が返された場合の処理を追加してください。
Please add handling for when an undefined value is returned.
Compound of 未 (not yet), 定義 (definition), and 値 (value). A straightforward technical term.