A general term for a device that mechanically processes an input string with the aim either of deciding whether it belongs to some set of strings (i.e. to a formal language) or of producing an output string.
There are two senses in which an automaton A is said to recognize (or accept) a language L: for any input string w,
Turing machines are a particular kind of automaton. Other kinds include the finite-state automaton, pushdown automaton, and linear-bounded automaton. Sequential machines are automata that produce an output string. According to the Church-Turing thesis, if a language is recognizable (in either of the above senses) by any kind of automaton, it is so recognizable by a Turing machine.