ERQI stands for EquiRatings Quality Index. It is a numeric value which indicates the likelihood of a horse completing the cross country phase of eventing without faults. It appears as a number between 0-1.
No, the ERQI attaches to the horse. Every horse has a different ERQI for different levels of competition. As the level of competition rises, so too does the risk. The ERQI reduces as the risk increases.