Noun. 1. scar tissue-the connective tissue that forms a scar; consists of fibroblasts in new scars and collagen fibers in old scars. connective tissue-tissue of mesodermal origin consisting of e.g. collagen fibroblasts and fatty cells; supports organs and fills spaces between them and forms tendons and ligaments. adhesion-a fibrous band of scar tissue that binds together normally separate anatomical structures.