The act of summoning one or more spirits with a predetermined purpose. The conjurer performs some type of ritual to call upon the spirit and often times this include using certain magic symbols drawn on the floor and/or altar. The conjurer will usually perform this at a specific time; Depending on what they are conjuring it could be done at a specific time during the day/night or according to the alignment of the planets. Incense, candles and potions are commonly used coupled with a specific spell to summon a spirit.
"Conjure" is also, in some regions, an alternative term for Hoodoo -- African-American folk magic -- that may or may not involve spirit-summoning.