From Halopedia, the Halo wiki
Sticky Arming refers to a setting in games of Assault. When arming a bomb, the amount of time it takes to arm the bomb is stored up as long as the bomb remains in the circle. For example, if one player begins arming the bomb and the time meter is filled half way when that one player dies, the next player that comes along and picks up the bomb only has to hold it within the circle for the remaining amount of time. This property is observed as long as the bomb remains in the circle after it is dropped.
A tactic often used involves one team charging a bomb that has been dropped in the circle and slowly arming it bit by bit, each player sacrificing his life in order to keep the bomb alive. As long as a team is able to continuously charge, pick up the bomb, and die without knocking the bomb out of the circle this tactic will work quite well.