Tissue

In medicine, tissue describes any set of similar cells that originate from the same source and perform a specific function. It's an intermediary level between a cell and an organ. Tissue is made of cells and organs are made of different tissues that are identical from person to person. The study of tissues is known histology.

Tissue is grouped into one of four types:

• Connective, which are cells separated from non-living tissue, such as blood (separated by plasma) or bone
• Muscle, which is capable of contraction to cause movement
• Nerve, which is capable of transmitting electrical potential
• Epithelial, which covers the surface of other tissues, such as skin

Tissue at Wikipedia