Medium Dependent Interface Cross-over. An Ethernet port connection where the internal transmit and receive lines are crossed.
An MDI port on a hub or media converter that implements an internal crossover function. This means that a "straight-through" patch cable can be used to connect a station to this port, since the required signal crossover is performed inside the port instead of in the cable.
Some hubs, including the Cisco 1528 Micro Hub 10/100, provide a media-dependent interface/media-dependent interface-crossover (MDI/MDI-X) button. This button is usually associated with a particular port. With this button set correctly, you can connect a network device to the associated port using a straight-through Ethernet cable rather than a crossover Ethernet cable.