implementation-defined behavior
Computing term for behavior that depends on the specific implementation (compiler, interpreter, etc.) and must be documented by the implementer.
In C, whether character types are signed is implementation-defined behavior.
Code that relies on implementation-defined behavior has low portability.
未定義の動作 (undefined behavior) is more severe: the standard imposes no requirements and anything can happen. 処理系定義の動作 requires the implementation to document its choice.
処理系依存 (implementation-dependent) is a broader term for anything that varies by implementation, not necessarily formally defined behavior.
Compound of 処理系 (implementation, processing system) + 定義 (definition) + の (possessive particle) + 動作 (behavior, operation). A direct translation of the English computing term 'implementation-defined behavior'.