An Abrasion Class (AC) rating is a measure of a floor's durability. Abrasion Classes range from AC1 to AC6, with AC6 being the most durable.
To determine a floor's AC rating, it undergoes a series of tests (conducted by an independent third-party) to determine the floor's resistance to abrasion, impact, stains, and burns. Tests can include rubbing sandpaper back and forth, moving furniture legs and chair wheels, exposure to heat and burns, exposure to moisture, impact resistance, staining, and more.
A 1-6 grade is given for each test, and the final score is based on the lowest score the floor receives. For example, if a floor received a score of 5 on every test except moving furniture, where it received a score of 3, you would see the floor rated as an AC3.
The Iona Mineral Core Tile Collection has an AC6 durability rating, the highest recognized grade in flooring.