Operators operate on operands.
Stated differently, operands are the things that are operated on by operators.
For example, in the following expression, the plus character is an operator while x and y are operands.
x + y
Assuming that x and y are numeric variables, this expression produces the sum of the values stored in the two variables.
The variable x would be called the left operand and the variable y would be called the right operand.