In particle physics, a Dirac fermion is a particle that is different from its antiparticle. This is true for most particles. In the standard model of physics, each particle has its antiparticle. 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. Neutrinos are particles without an electric charge, they might be Majorana fermions.