General definition:
* Tissue is a group of similar cells that work together to perform a specific function. This is the most basic and accurate definition.
More detailed descriptions:
* Tissue is a collection of cells of the same type that are organized together to perform a specialized function. This definition emphasizes the specialization and cooperation of cells within a tissue.
* Tissue is a level of organization in multicellular organisms that is composed of cells that share a common origin and function. This definition places tissue within the hierarchy of biological organization.
Specific examples:
* Epithelial tissue forms linings and coverings.
* Connective tissue supports and connects other tissues.
* Muscle tissue is responsible for movement.
* Nervous tissue transmits information throughout the body.
Ultimately, the "best" description depends on the intended audience and the specific purpose of the description. However, all descriptions should accurately convey the key features of tissues as groups of similar cells that work together to perform a specific function.