A polynomial expression is a mathematical expression that consists of variables, coefficients, and exponents combined using addition, subtraction, and multiplication. The variables are typically represented by letters, such as x or y, while the coefficients are numerical values. A polynomial can have one or more terms, and the highest exponent of the variable determines its degree. For example, in the polynomial expression 3x^2 + 2x + 1, the degree is 2. Polynomials are classified based on the number of terms they contain. A polynomial with one term is called a monomial, two terms is a binomial, and three terms is a trinomial. Polynomials are fundamental in algebra and are used in various fields, including science, engineering, and economics, to model relationships and solve equations.