A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. The series is specially designed for applications requiring higher brightness.
The "millimeter" size refers to the diameter of the LED. For example, if you need to drill a hole in a box for your 5mm blinky LED, the hole size should be 5mm, and you'd need a 5mm drill bit to make it. 5mm is the most common size you'll see, and they can be extremely bright!
A pack of 10 different colors (Red, Green, Blue, Yellow, and White) with 5mm LEDs, please note that the amount of each color is not set and is in random amounts making up 10 LEDs
5mm Led - Pack of 10 Specification:
Color: Green, Red, Blue, Yellow and white
Working Voltage: 2- 3V