Final answer:
An expression is a mathematical phrase that includes numbers, variables, and operation symbols. Variables can represent values in a range and are integral in forming expressions used in equations and modeling mathematical phenomena.
Step-by-step explanation:
An expression is a mathematical phrase that can contain ordinary numbers, variables (like x or y), and operators (like add, subtract, multiply, and divide). Variables are names given to quantities that may assume a range of values. For example, in the equation of a line, x and y are the variables, with x representing a value on the horizontal axis and y representing a value on the vertical axis, while b and m are coefficients that influence the slope and position of the line respectively. In a mathematical phrase, the variables and numbers are combined through the operations of addition, subtraction, multiplication, or division to form an expression. Understanding this concept is fundamental in the study of algebra and helps to build the foundation for more complex mathematical modeling.