The cell cycle is the regular pattern of growth, DNA duplication, and cell division that occurs in eukaryotic cells. It consists of four main stages: gap 1 (G1), synthesis (S), gap 2 (G2), and mitosis (M). The longest part of the cell cycle is interphase, which includes G1, S, and G2 where the cell grows in size, replicates its DNA, and undergoes further growth before division.