A quartic function is a polynomial function of degree four, meaning it has the general form $f(x) = ax^4 + bx^3 + cx^2 + dx + e$, where $a$, $b$, $c$, $d$, and $e$ are real numbers. Quartic functions are a specific type of polynomial function that are important in the study of graphs of polynomial functions and the determination of their zeros.