To answer the first part of your question (What is it?), it's part of the Automatic Climate Control that N. American cars don't have. On some people's vehicles, the system has a brain fart and looks for the outside ambient temperature sensor. When it doesn't find the sensor, you get the AMB and --- under it.
Non-N. Am vehicles can actually buy the sensor, plug it in and have the display actually work. We don't even have the wiring harness to plug into, though. :bs: