"Spike" Attacks are skills which allow for optimal DPS, with little/no regard for fuel regeneration (often because of a spammable recovery item or skills which allows them to get back MP/SP/TP etcetc). What enables this is usually a system of cooldowns which tries to balance extreme attacks with large cooldowns, and mid-high range damage attacks with higher fuel costs, but little extra cooldown. In the late-game of most MMORPGs these tend to dominate the "DPS" function and reduce the overall dynamic of the system to simple calculation over meaningful choice at the given circumstances.
Examples include RO's "Sonic Blow" for the Assassin-job or higher levels of Rogue skills in WoW. I believe there are several Guild Wars videos of players using "Spike Builds" during PvP sessions.
The point to make here is that for a battle system to be immersive, a player character cannot simply be a "tank" or "DPS" build and cooldowns create an almost turn-based effect which favors those who can output or take more in a set amount of time- creating a "speed" of sorts to the games involving them rather than a "tempo"
