expression
is something that; is that which
A formal or written explanatory phrase used to define or characterize the nature of something. Often found in definitions, explanations, or abstract statements.
言語とは、人間が互いに意思を伝えるためのものである。
Language is something that humans use to communicate with each other.
この規則は、安全を確保するためのものである。
This rule is something that ensures safety.