The term for a white, flattened, tendinous expansion that serves mainly to connect a muscle with the skeletal components it moves:

The term is - aponeurosis.

The aponeurosis is a flat ribbon or sheet of tendon like material that anchors a muscle or connects the muscle to the moving part. It is composed of dense fibrous connective tissue containing fibroblasts and bundles of collagenous fibers in ordered arrays. Structurally the aponeurosis is similar to tendons and ligaments.