A nixie tube is an electronic device for displaying numbers or other information, in the form of a glass tube containing multiple cathodes, a wire mesh anode, filled with neon and often a little mercury and/or argon at a small fraction of atmospheric pressure. The most common form has ten cathodes in the shapes of the numerals 0 to 9 (and occasionally a decimal point or two), but there are also some with various letters, signs and symbols. Each cathode can be made to glow by applying about 200V DC between it and the anode.

The device was developed in the 1950s by Haydu Brothers Laboratories and introduced by Burroughs Corporation, who owned the name Nixie as a trademark. Other similar devices that functioned in the same way, made by other manufacturers, were called by various trademarked names including Numicator and Digitron. The proper generic name is "cold-cathode neon readout tube", though the phrase "nixie tube" quickly entered the vernacular as a generic term. The devices were superseded in the 1970s by light-emitting diodess (LEDs).

According to an article in Scientific American magazine (June 1973, p66), the name was derived by Burroughs from "NIX I", an abbreviation of "Numeric Indicator eXperimental No. 1".