Martial Arts die?

[Orion Invictus]

I assumed this was my Monk level, but clearly it's not. So what is it?

[Northturtle11]

martial arts die is damage die that is used for monk specific actions that deal damaage, your fist, and monk weapons (basically anything you are proficient in that doesn't require two hands) if the damage die is better. your martial die increases at certain levels for example goes from 1d4 to 1d6 at level 3 or 5 I believe. at level 9 it becomes a 1d8. so if you have a weapon that normally have a weapon that deals like 1d4. It will get bumped to a 1d6/1d8 if it counts as a monk weapon for you.