Today it means: An abstract computing machine that has a finite number of possible internal states and operates on an infinite memory tape by first reading a symbol from a cell in the tape, and then, deterministically, based on that symbol and the machine’s state, writing a symbol in that cell, moving to a neighboring cell, and/or changing state. Full definition →
Named after English mathematician, logician, and cryptographer Alan Turing (1912–1954), who introduced the concept in 1936 to give a mathematically precise definition of computability. Turing called it an a-machine; the term "Turing machine" was coined by his doctoral advisor Alonzo Church.
Etymology from Wiktionary, CC BY-SA 4.0.