By the broadest definition, a composite material is one in which two or more materials that are different are combined to form a single structure with an identifiable interface. The properties of that new structure are dependent upon the properties of the constituent materials as well as the properties of the interface. Within the composite, it is still possible to easily tell the different materials apart. They do not tend to blend or dissolve into each other.
Composites have been used by humans for thousands of years. The most common primitive use was mud bricks, which was made of mud and straw. Today, you can see the applications in which composite materials are used. For example, our roadways are paved in either aggregate reinforced portland cement or asphalt concrete. You can also find examples in your home such as fiberglass tubs and synthetic granite or marble counter tops.
There are also composites found in nature. Examples of such are wood and human teeth.