According to the mathematical definition, an expression is an expression that uses symbols to express the relationship between numbers and operations, which usually includes operation symbols such as addition, subtraction, multiplication and division. For example, 2+3=5 is a formula, which means that the sum of 2 and 3 equals 5. A formula is a mathematical expression consisting of numbers, variables, operators and brackets, and can contain multiple expressions. For example, 3x+2y= 10 is a formula, where x and y are variables, representing unknowns, 3x and 2y are expressions, representing the product of variables and coefficients, and = 10 represents the equality relationship.