Mana is the mystical energy, a resource used to cast Miracles in Black & White 2.
It's the game's version of the original game's Prayer Power.
Mana manifests as a bright blue flame; a flame that burns on top of an Altar taller, brighter, and more intensely, the more total Mana is accumulated.
Mana can be obtained in two ways: through worship at a fully-built Altar (whether by Disciple worshipers, or generated automatically by idle, non-Disciple Villagers which opt to assume the role of their own volition), or sacrifice (by dropping people into the flame atop an Altar, which absorbs their lifeforce, in exchange giving you static amounts of mana, and increased reputation as an evil god.)
Unlike Altars, Epic Miracles have their own reservoir of Mana, which must be completely filled to charge an Epic Wonder before the miracle can be cast.