It is one of the classes available to you during Character Creation
The Conjurer is a defensive based caster. That means healer.
It has some DPS abilities that are there to encourage soloing play, but it shines through the multitude of healing and protection capabilities: Cure, Protect, Raise, Stoneskin, some iconic Final Fantasy abilities. The four abilities mentioned are actually transferable between the skills.
Traits take it a step further giving them quite useful effects. An ability like raise, transferable to everybody allows you to resurrect somebody, but as a conjurer you are able to resurrect somebody in combat.
Protect, normally just gives you a physical defense buff, but as a Conjurer it mixes protect and shell, giving you magic defense as well.
Overall this is a healing class, but with some DPS capability.