Fermions are particles which have half-integer spin and therefore are constrained by the Pauli exclusion principle.
A fermion is a fundamental type of particle in physics that is one of the two basic building blocks of all matter in the universe (the other being bosons).
Fermions have half-integer spin (e.g., 21, 23, 25, etc.) and obey Fermi-Dirac statistics. A key consequence of this is the Pauli Exclusion Principle, which states that no two identical fermions can occupy the same quantum state simultaneously. Examples of fundamental fermions include electrons, protons, neutrons, and quarks.