In physics, a Dirac fermion is a fermion which is not its own antiparticle. The vast majority of particles fall under this category, as they are not their own antiparticles, and in particle physics all fermions in the standard model, except possibly neutrinos, 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 is its own antiparticle.
In condensed matter physics, low-energy excitations in graphene and topological insulators, among others, are fermionic quasiparticles described by a pseudo-relativistic Dirac equation.