Definition: In a composite material, the structural reinforcement is held in place by matrix. In the case of fiber reinforced polymer (FRP) composites, structural fiber is surrounded by a matrix adding rigidity. Most often this matrix is a thermoplastic or thermosetting resin.
A matrix alone is not structural and is brittle. While a reinforcement alone is flimsy. But together, they form a strong composite.
Examples:
In concrete structures, the rebar is the reinforcement and the cement is the matrix.
