Landau Fermi liquid theory describes the behavior of interacting fermions at low temperatures, where the system can be understood in terms of quasiparticles that have a one-to-one correspondence with the non-interacting fermions. Despite interactions, these quasiparticles retain the Fermi-Dirac statistics and have well-defined properties such as effective mass and lifetime, allowing the prediction of various physical phenomena in metals and other systems.