Tissue is a group of cells that have similar structure and that function together as a unit. In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.
There are four main tissue types in the body: epithelial, connective, muscle, and nervous. Each is designed for specific functions.