A sealed glass tube containing a near-vacuum which allows the free passage of electric current.
 Example sentencesExamples
-  A photocell is usually a vacuum tube with two electrodes.
 -  I didn't know much about transistors because my education was during the days of vacuum tube.
 -  We think of the 1950s as the golden era of the vacuum tube.
 -  It wasn't until the vacuum tube and the transistor were invented that true computers became feasible.
 -  In 1948 the vacuum tube was replaced by longer-lived solid-state transistors, marking the dawn of microelectronics.