Tissue is a group of cells that work together to perform a specific function. There are four main types of tissues: epithelial, connective, muscle, and nervous tissue. Connective tissue provides structural support and connects other tissues throughout the body. It is made of cells, fibers, and extracellular matrix embedded in fluid. Connective tissue includes tendons, ligaments, adipose tissue, and blood. It has many important functions like connecting and protecting organs, storing energy, and providing a structural framework.