An algebraic expression is a combination of numbers, variables, and mathematical operations. Variables are symbols, often letters like x or y, that represent unknown values. For example, in the expression 3x + 5, 3 is a coefficient, x is the variable, and 5 is a constant. Algebraic expressions can be simplified or evaluated by substituting values for the variables. These expressions are used in various fields, including science, engineering, and finance, to model real-world situations. They help in solving equations and understanding relationships between quantities. Learning to manipulate algebraic expressions is a fundamental skill in algebra.