Hot zones are certain areas in RuneScape that are considered very dangerous on PvP worlds, as they are popular for players to come and kill each other. Many of these areas have monsters as well. A "flaming skull" icon will appear on the screen to notify players when they enter these areas.
Hot zones give players an advantage because there is a higher chance for killed opponents to drop better items in these areas, as opposed to killing players outside the hot zones. Hot zones are more dangerous, however, due to the larger number of players in these areas who will hunt almost any players who wander into the area for the improved drops they can get.
Also, Hot zones give more earning potential (EP) than non-hot zones. In a hot zone, you can gain a maximum of 25% EP per half an hour, while a regular spot gives a maximum of only 15%.