Dynamos are systems or mechanisms that produce electric currents and magnetic fields through the motion of conductive materials. In the context of celestial bodies like planets or stars, dynamos refer to the process by which a rotating, convecting, and electrically conducting fluid generates a self-sustaining magnetic field. This process occurs in the fluid layers of these bodies, typically the outer core, where the movement of conductive materials, such as molten iron or nickel, creates electric currents through electromagnetic induction. These currents generate a magnetic field through a self-exciting mechanism known as the dynamo effect.