The expression (x + y)^n represents the binomial expansion, which is a way to expand expressions that are raised to a power. Here, x and y are variables, and n is a non-negative integer. The expansion can be calculated using the Binomial Theorem, which states that (x + y)^n can be expressed as a sum of terms involving combinations of x and y. Each term in the expansion is formed by multiplying x and y raised to different powers, specifically x^n-ky^k, where k ranges from 0 to n. The coefficients of these terms are given by the binomial coefficients, which can be calculated using combinations. This expansion is useful in various fields, including algebra and probability.