The MAPK pathway, or Mitogen-Activated Protein Kinase pathway, is a crucial signaling cascade in cells that helps regulate various cellular processes, including growth, differentiation, and response to stress. It involves a series of protein kinases that activate each other in a specific sequence, ultimately leading to the activation of transcription factors that influence gene expression. This pathway is typically activated by external signals, such as growth factors or cytokines, which bind to cell surface receptors. Once activated, the MAPK pathway can trigger a range of cellular responses, making it essential for normal cellular function and development, as well as for understanding diseases like cancer.