Mostly obsolete, a storage tube is a special monochromatic CRT whose screen has a kind of 'memory' (hence the name): when a portion of the screen is illuminated by the CRT's electron gun, it stays lit until a screen erase command is given. Thus, screen update commands need only be sent once and this allows the use of a slower data connection, typically serial—a feature very well adapted to computer terminal use in 1960s and 70s computing. The two main advantages were:
Generally speaking, storage tubes could be divided into two categories. In the more common category, they were only capable of storing "binary" images; any given point on the screen was either illuminated or dark. The Tektronix Direct-View Bistable Storage Tube was perhaps the most-famous example in this category. Other storage tubes were able to store greyscale/halftoned images; the tradeoff was usually a much-reduced storage time.
Two pioneering storage tube displays were MIT Project MAC's ARDS (Advanced Remote Display Station) which used a Tektronix type 611 storage display unit and Tektronix's 4014 terminal, the latter becoming a de facto computer terminal standard some time after its introduction (later being emulated by other systems due to this status).