The number is the size. 0805 (imperial) is 0.08" x 0.05".
It's metric equivalent is 2012 or 2 x 1.2 mm.
Google "SMD sizes", and go to images for charts.
Most Arduinos have a 1k resistor array for the LEDs, so about 3mA.
But I noticed that the ProMini uses 10k (~0.3mA).
Much better I think. Small LEDs can be like lasers.
So bright that you can't see the writing on the board next to it.
Leo..