AVCMOS name/design came in from one of the companies Cypress acquired, IMI. It is another name for variable output impedance (VOI), or sometimes called variable slew rate (VSR). It is a type of output buffer that has a strong drive current from the beginning of a switch (ie. rise or fall time) to about the mid-point of the switch. At about mid-point, some of the legs of the transistors shut off so that the drive current is reduced, and the resulting transition from mid-point of the switch to the final settling value is smooth (i.e. little overshoot/undershoot). This way, higher frequencies can be achieved without as much overshoot/undershoot. It's called "variable impedance" because the impedance changed depending on whether you're looking at the start of the rise/fall time or the end. Actually, "variable slew rate" is perhaps a more accurate description.
Check the KnowledgeBase Article Titled: AVCMOS Outputs of CY2CC810 Explained at: http://www.cypress.com/?id=4&rID=39987