The Cylon data port is a device used by Cylons to access information in their datastream, as well as control various other Cylon technologies. Cylon agents need only to place their palm on the port and they are able to instantly access the data stream (Exodus, Part I).
Sharon Agathon attempts a rough version of this technique with Colonial technology by inserting a fiber optic cable into her arm, thus allowing her connectivity to Galactica's computer mainframe (Flight of the Phoenix).