What is "oracle machine"

n. (context computing theory English) In computability theory, a form of theoretical Turing machine, able to decide certain decision problems in a single operation.

In complexity theory and computability theory, an oracle machine is an abstract machine used to study decision problems. It can be visualized as a Turing machine with a black box, called an oracle, which is able to solve certain decision problems in a single operation. The problem can be of any complexity class. Even undecidable problems, like the halting problem, can be used.