What is the definition or description of: amyloid?

A protein : Amyloid is a kind of protein which can build up and accumulate in tissues and organs causing the organ to fail. The disease called amyloidosis occurs when the amyloid buildup causes organ problems. It may be seen associated with other diseases such as multiple myeloma, and can occur on its own. In alzheimer's disease amyloid can build up in the brain and brain blood vessels as well.