A duplex communication system is a point-to-point system composed of two connected parties or devices that can communicate with one another in both directions. "Duplex" comes from "duo" that means "double", and "plex" that means "structure" or "parts of"; thus, a duplex system has two clearly defined data transmissions, with each path carrying information in only one direction: A to B over one path, and B to A over the other. There are two types of duplex communication systems: full-Duplex and half-Duplex.