Battle for survival

From WoWWiki

Boss fights where individual player survival is the most important aspect are called Battle for Survival.

Some fights require all raid members to learn how to evade damage, and/or force the healers to keep the whole raid up. Typically such fights have long enrage timers (or none at all), and sometimes random or hard to control aggro. They are the most difficult type of encounter, because all raid members must learn something new. Battles for Survival remain a challenge even for well-geared groups, although good gear usually allows for a larger margin of error.

Some players consider Battles for Survival to be the most interesting type of fight, others hate them because they're inherently more difficult. Usually, they're found near the end of instances, most end bosses have at least one phase which is designed as a Battle for Survival.

Example: Shade of Aran, Magtheridon, Archimonde