The expression "n(n-1)" represents a mathematical formula where "n" is a variable that can take on any integer value. This expression is often used in combinatorics, which is the branch of mathematics dealing with counting and arrangements. Specifically, it calculates the number of ways to choose 2 items from a set of "n" items without regard to the order of selection. When you expand "n(n-1)", it simplifies to "n² - n". This shows that the expression is quadratic in nature, meaning its graph is a parabola. Understanding this formula is essential for solving problems related to permutations and combinations, which are foundational concepts in mathematics and statistics.