A trinomial is a type of polynomial that consists of three terms. These terms can include variables, coefficients, and constants, and they are typically combined using addition or subtraction. An example of a trinomial is x^2 + 5x + 6, where x is the variable, and 5 and 6 are coefficients. Trinomials can be classified based on their degree, which is determined by the highest exponent of the variable. The most common form of a trinomial is a quadratic trinomial, which has a degree of 2. Trinomials are often used in algebra for factoring, solving equations, and graphing functions.