What does "Electronic Ready" mean on a Giant Frame?
Based on comparison with the Giant Defy Advanced line, it seems to mean that you can run an electronic drivetrain (such as Shimano Di2 parts) - you have to mount things like a battery in order for the shifters to work and what not, so the frame will need to have the wiring harnesses and battery pack mounted.

This link shows the TCR line in 2012 with this done. 

What does an electronic drive train mean for most people? Likely, just an emptier wallet. But thats a different question all together.