DR means Damage Reduction.
Damage Reduction is a stat that reduces damage by a percent from all attacks (physical and magical- even skills). It can be only increased by the DEX stat. The x percent of the damage reduced is similar to the x number of DR stat (20 DR means 20% damage reduction). Thus, it reduces all damage, except from negative status (i.e. poison, lasting fire and bleeding). On 90 DEX, characters have 30% Damage Reduction.