Composites are mixtures of materials which give improved properties. One of the materials is the matrix or binding chemical and the other is the reinforcer. A good example is GRP - glass reinforced polyester(plastic) resin. where the glass fibres increase the strength of the polyester resin. Carbon fibre reinforced epoxy resin is stronger and lighter than steel.
Concrete is a composite (the cement is the matrix and the gravel and steel rods are the reinforcer) as are bricks made from clay reinforced with straw.
Natural composites include wood, shell and bone.
Car bodies - especially sports cars, F1 racing cars, boat hulls, lightweight struts and supports in bridge building and the construction industry. Aerospace - use of carbon fibre composites as well as high tech ceramic parts has revolutionised this industry.