Dirac fermions are particles that obey the Dirac equation, which describes the behavior of fermions with relativistic effects. They are characterized by having a linear energy-momentum relationship, meaning their energy increases linearly with momentum. This unique property leads to interesting phenomena, such as high mobility and low effective mass, making them important in condensed matter physics. In materials like graphene, Dirac fermions behave as if they are massless, allowing them to move at high speeds. Their unusual properties have potential applications in electronics, spintronics, and quantum computing, where they could enable faster and more efficient devices.