The term used for a group of cells that perform a specific function is "tissue." Tissues are organized into four main categories: epithelial, connective, muscle, and nervous tissue. Each type of tissue has distinct roles within the body. For instance, epithelial tissue covers surfaces and lines cavities, connective tissue supports and binds other tissues, muscle tissue facilitates movement, and nervous tissue transmits signals throughout the body. Understanding tissues is essential in biology and medicine, as they form the foundation of organ systems and play crucial roles in overall health.