W-Summon is a command ability exclusive to the W-Summon Materia, obtained from the Battle Square. It allows the user to summon two summons consecutively. If the Summon Materia is linked with Quadra Magic, using it with W-Summon can result in eight consecutive summons (excepting Knights of Round).
Evocation is the act of calling upon or summoning a spirit, demon, god or other supernatural agent, in the Western mystery tradition. Comparable practices exist in many religions and magical traditions and may employ the use of mind-altering substances with and without uttered word formulas.