a particle-reinforced composite

Instead of long fibers, the reinforcement is roughly equiaxed particles, like gravel, ceramic grains, or fine oxide dust, scattered through the matrix. Concrete (gravel and sand in cement) is the everyday giant example; so is the tungsten-carbide-in-cobalt of a drill tip.

There are two types. Large-particle composites: the particles are big enough that they simply restrain the matrix mechanically and share load by the rule of mixtures, as in concrete, cermets (ceramic plus metal, e.g. cemented carbide WC-Co in cutting tools), and metal-filled polymers. Dispersion-strengthened composites: very fine, hard particles (tens of nanometres, a few percent by volume, e.g. thoria in nickel or Al2O3 in aluminum) block dislocation motion much like precipitation hardening, but because the particles are inert and stable, the strengthening survives high temperature.

Particle composites are usually roughly isotropic (properties similar in all directions), and are cheaper and easier to make than fiber composites, letting you tune stiffness, wear resistance, or thermal expansion. They typically give smaller property gains than aligned fibers, but with far less directionality and cost.