In physics, a Dirac fermion is spin 1⁄2 particle (a fermion) which is different from its antiparticle. The vast majority of particles – perhaps all – fall under this category.
In particle physics all fermions in the standard model have distinct antiparticles (perhaps excepting neutrinos) and hence are Dirac fermions. They are named for Paul Dirac, and can be modeled with the Dirac equation.
A Dirac fermion is equivalent to two Weyl fermions. The counterpart to a Dirac fermion is a Majorana fermion, a particle that must be its own antiparticle.