I'm using the Asus X99-DELUXE-II motherboard:
It stands for High Amperage Fan. There should be a header (pins) on the board for you to plug in multiple fans or fans that are higher current. H-Amp fans usually have better cooling.
The manual setting for that board would allow you to set measure points and min/max temperatures, etc.
Search "High AMP" at this Asus page: https://www.asus.com/us/Motherboards/ROG-RAMPAGE-V-EDITION-10/