Summarised from: http://en.wikipedia.org/wiki/Nexus_7_%282012_version%29
The Nexus 7 is a tablet computer developed by Google in conjunction with ASUSTeK Computer Inc. (ASUS).
It was the first tablet in the Google Nexus series of consumer devices built by an original equipment manufacturer ('OEM') partner.
The June 2012 Nexus 7 features a 7-inch (180 mm) display, an Nvidia Tegra 3 quad-core chip, 1GB memory, Wi-Fi and near field communication connectivity, and 8, 16 or 32 GB of storage.
The tablet was also the first device to ship with version 4.1 of Android, nicknamed "Jelly Bean".
UPDATE: (August 2013)
A new July 2013 model has now been released, with a higher resolution screen, Snapdragon processor and much faster graphics processing.
This device ships with Android 4.3, available as an upgrade for the original (2012) Nexus 7.
UPDATE: (March 2014)
Both version not support OTA (over the air) update to 4.4.2 ('KitKat+).