Fermi arcs are surface states that appear in certain materials known as topological insulators. They are associated with the electronic structure of these materials, where the surface states connect points in the bulk electronic structure called the Fermi surface. This phenomenon is particularly observed in systems with strong spin-orbit coupling. These arcs are significant because they reveal unique properties of the material, such as spin-momentum locking, where the spin of electrons is linked to their momentum. This can lead to potential applications in spintronics, where the spin of electrons is utilized for information processing and storage.