Hello, It means that the rear oxygen sensor value is lower than the engine computer expects it should be.

I'd primarily suspect either a skewed front or rear oxygen sensor, but the problem could be caused by an exhaust leak or faulty catalytic converter as well, according to the shop manual.

It you're under 60,000 miles, take it in to the dealer for warranty service and let them figure it out. Based on the code definition, this could be difficult to diagnose.

You have 2 o2 sensors in the exhaust. One before the cat converter and one after. The o2 sensors sniff the exhaust and send signals to computer to adjust fule mixture.
If the senors ahve different readings from each other, either one is bad etc.. The only way to confirm what is happening is to have car hooked up to a scanner and watch the millisecond o2 sensor readings to see which one is bad.

This code will not affect the way the engine runs. You gas milegae could go down slightly. Without the scanner readings i can only tell you what the code means, not the exact solution to the problem