“Uno” means one in Italian and was chosen to mark the release of Arduino Software (IDE) 1.0. The Uno board and version 1.0 of Arduino Software (IDE) were the reference versions of Arduino, now evolved into newer releases. The Uno board is the first in a series of USB Arduino boards and serves as the reference model for the Arduino platform; for an extensive list of current, past, or outdated boards, see the Arduino index of boards.
 
Tech Specs 
Microcontroller: ATmega328P
Operating Voltage: 5V
Input Voltage (Recommended): 7-12V
Input Voltage (Limit): 6-20V
Digital I/O Pins: 14 (6 provide PWM output)
PWM Digital I/O Pins: 6
Analog Input Pins: 6
DC Current per I/O Pin: 20 mA
DC Current for 3.3V Pin: 50 mA
Flash Memory: 32 KB (ATmega328P), of which 0.5 KB is used by bootloader
SRAM: 2 KB (ATmega328P)
EEPROM: 1 KB (ATmega328P)
Clock Speed: 16 MHz
LED_BUILTIN: 13
Length: 68.6 mm
Width: 53.4 mm
Weight: 25 g