Noun, pl. collagens
1. A group of naturally occurring proteins found in animals, especially in the flesh and connective tissues of vertebrates. It is the main component of connective tissue, and is the most abundant protein in mammals, making up about 25% to 35% of the whole-body protein content. Collagen, in the form of elongated fibrils, is mostly found in fibrous tissues such as tendon, ligament and skin, and is also abundant in cornea, cartilage, bone, blood vessels, the gut, and intervertebral disc. (wikipedia.org)
Any of more than 28 types of glycoprotein that forms elongated fibers, usually found in the extracellular matrix of connective tissue.
3. A fibrous scleroprotein in bone and cartilage and tendon and other connective tissue; yields gelatin on boiling. (wordnetweb.princeton.edu)
4. The main structural protein found in animal connective tissue, yielding gelatin when boiled. (Google Dictionary)
5. (Science: protein)
The protein substance of the white fibres (collagenous fibres) of skin, tendon, bone, cartilage and all other connective tissue, composed of molecules of tropocollagen, it is converted into gelatin by boiling. Collagenous pertaining to collagen, forming or producing collagen. (biology-online.org)