bound variable
Technical term in logic and formal semantics. Refers to a variable that is quantified or otherwise bound by an operator, as opposed to a free variable.
A bound variable is a variable within the scope of a quantifier.
In this logical formula, x is a bound variable and y is a free variable.
自由変項 (free variable) is the opposite of 束縛変項; it is not bound by any quantifier or operator.
量化子 (quantifier) is the operator that binds variables, such as ∀ or ∃.
Compound of 束縛 (sokubaku, 'binding') and 変項 (henkō, 'variable'), a calque from English 'bound variable'.