Phantom circuit refers to a connection that appears to be permanent between two devices, but does not actually exist. This term is commonly used in the field of electronics, telecommunications, and networks. However, there are some synonyms that can be used to describe phantom circuits such as virtual circuit, ghost circuit, and transparent circuit. A virtual circuit is a circuit that appears to be a physical circuit but is actually a logical circuit. A ghost circuit also refers to a connection that is not physically present. Finally, a transparent circuit is a circuit that allows data to pass through without affecting it. These synonyms can be used interchangeably depending on the context.