MP, also known as Mana or Magic Point, is a (magical) power resource available to casters which they draw upon when casting spells. In Dragonica, it's available to all classes and are needed to use skills. The amount of MP currently available to the caster is denoted with a special blue MP bar below their health bar. By default, casters start with a full bar of mana which is then depleted as they cast spells.
Characters have an innate replenishment of both health and mana. The rate at which these two stats replenish is based on a character's strength and intellect. There are also some Skills that can raise the replenishment rate for these stats independently. MP regeneration itself is slow without skills, but MP can be replenished instantly during combat using MP potions.
The maximum amount of MP available to a caster is determined by a combination of the character's class, level and their Intellect. In addition, some items grant MP bonuses. Finally, items can be refined to give additional increases to MP.
Base MP is a term used to refer how much MP a character has before it is modified by Intellect and other Item Effects. Some spells require a percentage of your base MP to be cast.