Arranged in a 4x4 matrix, each pixel is individually addressable. Only one microcontroller pin is required to control all the LEDs, and you get 24 bit color for each LED. Multiple matrices can be daisy chained together assuming that you supply enough current.
Please refer to the Adafruit NeoPixel Uberguide for instructions
Size: 30 x 30 mm
See datasheet for each LED for more detailed info.