What refers to the discharge of electricity through a gas-filled electron tube?

The discharge of electricity through a gas-filled electron tube is referred to as glow discharge. This phenomenon occurs when a voltage is applied across the electrodes within the tube, causing ionization of the gas and resulting in a visible glow. During glow discharge, positive ions are attracted to the cathode while electrons are propelled toward the anode, leading to a flow of current through the gas. This process is utilized in various applications, including gas discharge lamps, neon signs, and certain types of plasma displays, highlighting the importance of glow discharge in practical electronics and optics.

The other options, while related to electron movement, refer to different processes. Field emission involves the quantum mechanical tunneling of electrons from a solid surface, thermal emission refers to the release of electrons from a material due to thermal energy, and the photoelectric effect describes the release of electrons from a material when it absorbs light. Each of these processes operates under different principles and conditions, distinguishing them from glow discharge.