well-formed formula

well-formed formula (plural well-formed formulas or well-formed formulae)

1. (logic) A statement that is expressed in a valid, syntactically correct, manner.

   This program works correctly on all well-formed formulas but it blows up on illegal input.

• wff, WFF

• axiom

• symbols

• formal language

• well-posed

•   well-formed formula on Wikipedia.Wikipedia