The document defines sinusoidal functions as functions that can be written in the form f(x) = asin(bx - c) + d or f(x) = acos(bx - c) + d, where a, b, c, and d are real numbers. It lists some key properties of sinusoidal functions, including their period (2π/b), amplitude (a), and phase shift (-c/b). It provides examples of sketching sinusoidal functions and determining their properties based on given equations or graphs.