[quote]There are different types of magic that each user typically will only master one type of magic. The Arcane stream is the standard people like Merlin, Mages, Sorcerers all tap into it. The Arcane Stream is the magic of Merlin and other sorcerers that can be molded into various effects. The Beyond is the amalgamation of an realm of arcane energy that grasps several dimensions. Dimensional Planes are connected by magical leylines. Merlin uses wards and magical locations to stop dimensional bleeding. - Gowi[/quote]

I realized I kind of explained this like shit.

But basically the Arcane Stream is the magical energy that lies [i]between[/i] dimensional planes as a sort of “distortion” created. If kept unmonitored or uncontained it can cause massive rifts where a demon or eldritch horror can just walk out of their world and into ours. That’s where Merlin’s job comes in— to keep things safe from magical harm and to contain anything that slips through the cracks (because even Merlin cannot buff out arcane magic). 

This energy can be used to create anything since it is dimensional magic in nature— hence arcane.

The Arcane Stream / The Beyond are two terminologies coined by Merlin and carried on by others later in history to have a word for the energy between worlds that run through the planet at key points like magical highways (leylines).