Fermions are a category of elementary particles that follow the Fermi-Dirac statistics, which describe particles with half-integer spins. The fundamental distinction between quarks and leptons lies in their interactions and their participation in the strong nuclear force.
Quarks are the elementary particles that interact through all four fundamental forces: the strong nuclear force, electromagnetic force, weak nuclear force, and gravity (although gravity is not fully understood within the framework of particle physics). Quarks are subject to the strong force, which is mediated by gluons, and they carry a fractional electric charge (either +2/3e or -1/3e). They are the building blocks of hadrons, such as protons and neutrons.
Leptons, on the other hand, do not participate in the strong nuclear force. They only interact through the electromagnetic force, weak nuclear force, and gravity. Leptons carry integer electric charges (either 0e or -1e) and do not experience the strong force. Examples of leptons include electrons, muons, taus, and their associated neutrinos.
The distinction between quarks and leptons is based on their fundamental interactions and the forces they experience. Quarks have the ability to participate in the strong force and form bound states, whereas leptons do not experience the strong force and exist as individual particles. This fundamental difference in their interactions and behaviors sets quarks apart from leptons within the framework of the Standard Model of particle physics.