RvR  

Warhammer Online Wikibase™ Dictionary

RvR, or Realm vs Realm, is a fully integrated PvP experience in WAR. It is the ongoing struggle between the forces of Order and Destruction. Each zone has sub-zones of both PvE and RvR content. It is estimated that the ratio of PvE to RvR content will be 4:1 at tier 1 and 1:4 at tier 4.

Some servers are designated as Open RvR, meaning simply that you are flagged for RvR the moment you login rather than only by actions or by entering a Scenario or RvR Lake, meaning you can be attacked by any enemy player at any time. Fortunately, the Chicken rule still applies preventing high-level players from griefing in low-level zones.