In programming, an expression is any legal combination of symbols that represents a value. Each programming language and application has its own rules for what is legal and illegal. For example, in the C language x+5 is an expression, as is the character string "MONKEYS."
x + 5
x and 5 are operands, and + is an operator.
Expressions are used in programming languages, database systems, and spreadsheet applications. For example, in database systems, you use expressions to specify which information you want to see. These types of expressions are called queries.
Expressions are often classified by the type of value that they represent. For example: