Spike Damage, or a damage spike, is a massive amount of damage dealt to a single target over a very short period of time.
Spike damage may come in the form of one powerful skill, such as Obsidian Flame, or from a fast successive skill combo, such as a knockdown followed by Aftershock. Spikes often come from multiple damage sources hitting simultaneously, such as being the focus fire of six attackers or running into 20 traps overlapping each other. Spike Damage is effective against enemies that rely heavily on health regeneration skills, since the foe takes damage faster than they can recover.
Spike healing counters spike damage by rapidly healing the amount of health that was lost, but depends on the reaction speed of the healer. Healing too slowly won't keep the target alive, while healing too quickly often results in over-healing before the majority of the multi-source spike damage comes in.
Builds focused on spike damage usually have a lower average DPS in the long run, due to balancing factors such as long activation/recharge times, exhaustion, and energy costs.
Some forms of spiking exhaust the initial resources of a player or team, such as lowering an Elementalist's maximum energy, or depleting the energy of any class. The spiking team usually hopes to kill an enemy with those initial resources, giving a great advantage despite not being able to maintain the initially high rate of damage.
Other kinds of spike teams deal erratic damage, doing low or no damage for long periods, punctuated by sudden spikes in the amount of damage being done, overwhelming enemy healers.