Ramp

In healing, a ramp is a process where healing buffs are applied at a precise timing, which leads into the potential for a large amount of burst healing. Usually a cast sequence is used to ensure exact and reliable timing of the application of these healing buffs and also generate some sort of buff extension. In some cases once the damage has been received from the boss, then a second cast sequence may be used to activate the healing of these buffs.
Healing ramps are a key part of the Discipline priest, Mistweaver monk, Restoration druid and Preservation evoker playstyles. A list of these specializations and some examples of of their key abilities or talents during a ramp follows (not an exhaustive list of all options):
Spec 	Buff 	Extension/Application 	Activation
Discipline 	Atonement 	Evangelism</br>Rapture 	Damage (eg Schism)
Mistweaver 	Renewing Mist	Rising Mist</br>Rapid Diffusion	Vivify
Restoration Druid	Rejuvenation 	Luxuriant Soil</br>Flourish 	Flourish
Preservation 	Lifebind 	Resonating Sphere</br>Stasis 	Emerald Communion
Holy priests, Holy paladins, and Restoration shamans are generally not considered ramp healers, as their abilities generally do not require an exact cast sequence to be timed leading up to a damage event. This does not necessarily mean that non-ramp healers cannot do burst healing. However, the mechanism by which those specializations perform it will be different to that of the ramp specializations.
Ramps tended to come into their modern forms around Legion. For example, this was the introduction of Power Word: Radiance which more rapidly applied Atonement to more targets than previous options.