An expression is a number, a variable, or a combination of numbers and variables and operation symbols. An equation is made up of two expressions connected by an equal sign. An inequality is used in a...An expression is a number, a variable, or a combination of numbers and variables and operation symbols. An equation is made up of two expressions connected by an equal sign. An inequality is used in algebra to compare two quantities that have different values. Exponential notation is used in algebra to represent a quantity multiplied by itself several times.