Magic spells are potent, perhaps innate abilities which certain characters; (playable or non-playable) have access to. Some examples of this is in castlevania portrait of ruin, charlotte, (a descendent of the Belnades clan which is a clan believed to help fight side by side with the Belmont clan) a witch who specialises in magical attacks to deal devastating damage or cure the team with healing spells. Some of these include shooting magic or curing poison charlotte automatically has magical powers due to her Belnades' bloodline however she further expands on them by reading heavily and is considered smarter of the two playable characters.
An example of magic that isn't considered innate may be Dracula's magic, as it is aforementioned in previous castlevania games that he stole his power, however one could interpret that the attacks he uses in battle may look similar to magic, an example of this may be when he shoots out bats or calls fourth bats.
Another example where magic is seen is in one of the earlier castlevania games (symphony of the night) by Sypha Belnades. She is by bloodline a witch and so has access to powerful spells such as transformation, being able to call fourth fire, ice and lightning and being able to hurl them from her fingertips.
Also it is mentioned in castlevania dawn of sorrow that the main antagonist Celia Fortner exorcises great magical power, this is evident in the way in which she is able to summon forth a replica of Dracula's castle. It is also evident as she is able to summon powerful monsters (demons) such as angiuni the demon of fire and to fuse it unto one of her candidates (Dario Bossi) later in the game.
Overall, there are many types and forms of magic within the series and it is evident that whilst this is inherit by most characters it is also evident that some gain it though other means. Perhaps through magical items and other power enhancing talismans of that ilk.