The Nexus S is the second generation in a line of smartphones that are in direct collaboration with Google. This time, it's made by Samsung as opposed to the Nexus One from HTC. Google's Nexus line of phones are always a stock, vanilla Android experience with none of the custom overlays or UI's that manufacturers sometimes install on their phones.
This was the first device to launch with Android 2.3 Gingerbread for the masses. It sports a 4-inch Super AMOLED touchscreen, 16 GB of internal memory (no expandable memory), a 1Ghz Hummingbird processor and NFC chip for making purchases directly using your handset.
This phone was seen by many as not really a successor to, but as a variant of the Nexus One - hence the "S" in the title and not an official "Two."