What is the smallest subatomic particle?

The smallest subatomic particle is the quark. Quarks make up larger subatomic particles called hadrons, which include baryons and mesons. Three quarks make up composite particles called baryons, and the combination of a quark and an antiquark comprise a meson.

Quarks are fundamental particles and cannot be reduced any further into smaller particles. They are the building blocks of all the particles that make up matter. They come in six varieties, also called flavors. These flavors only occur in certain specific pairs; these pairs are known as the top and bottom quarks, up and down quarks and the charm and strange quarks.