In biological terms, a tissue refers to a group or collection of similar cells that work together to perform a specific function within an organism. These cells are often organized in a structural manner and have a shared purpose or function.

There are four primary types of tissues in animals:

1. Epithelial Tissue: This tissue covers the surfaces of the body, both externally and internally. It serves as a protective barrier and can also perform functions like absorption and secretion.

2. Connective Tissue: Connective tissues support, bind, and protect other tissues and organs in the body. Examples include bone, cartilage, blood, adipose tissue (fat), and tendons.

3. Muscle Tissue: Muscle tissue is responsible for movement. There are three types of muscle tissue: skeletal muscle (voluntary movement), cardiac muscle (found in the heart), and smooth muscle (involuntary movement, like in the digestive system).

4. Nervous Tissue: Nervous tissue is involved in transmitting electrical impulses and allows for communication within the body. It forms the nervous system, including the brain, spinal cord, and nerves.