The Arduino UNO R3 is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. Arduino UNO differs from all preceding boards because it does not use the FTDI USB-to-serial driver chip.
Additional features coming with the REV3 version are:
Find here more informations (including the tech specs) about the Arduino Uno.
"Uno" means "One" in Italian and is named to mark the release of Arduino 1.0. The Uno and version 1.0 are the reference versions of Arduino. The Uno is the reference footprint model for the Arduino platform.