n. 1. any sequence of symbols of a formal calculus, whether or not complying with the formation rules of that theory, such as
) 5 ) + 7 ×
in elementary arithmetic. 2. such a sequence that is syntactically correct; a sentence or well-formed formula of any formal theory. 3. a formal expression of some rule or other result, such as Stirling's formula or Frenet formulae.