1. a quantity upon which a mathematical operation is performed;

The Collaborative International Dictionary of English v.0.48:

Operand \Op"er*and\, n. [From neuter of L. operandus, gerundive of operari. See Operate.] (Math.) The symbol, quantity, or thing upon which a mathematical operation is performed; -- called also faciend. [1913 Webster]WordNet (r) 3.0 (2006):

operand n 1: a quantity upon which a mathematical operation is performedThe Free On-line Dictionary of Computing (30 December 2018):

operandAn argument of an operator or of a machine language instruction. (1995-08-18)