It's a popular microcontroller board based on the ATmega328P microcontroller. 

It features 14 digital input/output pins (6 of which can be used as PWM outputs) and 6 analog inputs. 

It has a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button. 

The Uno R3 SMD version, as seen in the image, has the ATmega328 microprocessor chip integrated and soldered onto the board, unlike the standard Uno where it's removable. 

It's widely used for various electronics projects and is considered a great starting point for beginners in microcontrollers.