Count : To count means to find out the number of objects by adding one for every object.

Number : A number $x$ is a mathematical symbol representing a quantity.

Foot : A foot or ft is a unit for measuring length. 3 feet are one yard. 1 foot is about 30 $cm.$

Inch : An inch or $in$ is a unit of measurement for length. 12 inches are one foot and 1 inch is about 2.54 $cm.$

Expression : An expression is a succession of constants, variables and mathematical operations that if evaluated for specific values of the variables represents a number.

Variable : A letter in an expression or function that represents an arbitrary number.