Seriously, what is it? I was flipping through my books, and it's in both SR4A and the regular version with no explanation (Combat Mage sample character). I can't think of anything in it that wouldn't be covered by Magic Theory, and there isn't really any explanation. Same goes for Phenomenon; isn't that the sort of thing covered by Theory?

Ideas?

I'm surmising that "Magic Background" means that the character recieved some magickal teaching/training at an early age (recognised for his Talent by a corprate sponsor, or one of his/her parents was a Mage) and gravitated toward the Combat Mage archetype that he/she today.

I would consider Magic Theory to be the book learning and academic knowledge knowledge that a character has from study such as all spell forumula from norse traditions use the Sig rune, or that Mero can't live in fresh-water.

Magic Background would be things like: Don't say the "kerfulffle" in front of a mystic crusader because it will piss them off, or that for some reason ghouls are driven batty when you sing Shield Wall songs at them. Essentially stuff that you would learn from experience that can't be quantified in a book or knowsoft.

Think of it as an all encompassing knowledge skill for that subject. Not as in detail as magic theory, but covering many more pieces of subject material, from theory, history, usage, the planes, materials, you get the idea.

I've never heard of this skill and never read the archetyp in detail. Some skill suggestions that might be included in "Magic Background" apart from Magic Theorie:

Parabotany
Parazoology
Magical Phenomenos
Spirits / Astral Beings
Astral Constructions
Astral Phenomenos
Metaplanes
Places of Power
Magical Traditions / Specific Rituals
Historical Magic (5th World)
History of Magic / the Awakening
The 4th World / Artifacts of the 4th World
Magic and Law
Magic and Society

Probably it boils down to :

Magic Theory : Academic Knowledge
Magic Background : Professional Knowledge

So Magic Theory would encompass what you learn about magic in a thaumaturgy class at a university, whereas Magic Background would rather be applied knowledge picked up during a practical magical education.

It is the difference between having a Degree and OJT (On Job Training). There are certain things your going to pick up that can't be taught in a book, and there are individuals that would never have a chance (or choose not to) to pick up information from a book (example a tribal shaman). A character with just Magical Background would more then likely be either a street mage or follow some more naturalistic magic path. A character with both Magical Theory and Magical Background would be a seasoned magical user (learned the stuff and then actually put it to use), and a character with just Magical Theory would be more of a book worm.

If you read more about just Knowledge skills and the different knowledge skill categories (street, background, academic, etc) it makes more sense. It is roughly the same knowledge that comes from different sources (same *&^% different pile).

Magic Theory is the "Theory" of how magic works. It is academic in nature, dealing with the structure of magic and its core rules. It does not include any flavor or history. You would use this when trying to design a new spell or ritual. If used to identify a spell, it would be a scientific identification. "That would be an elemental creation spell, focused on force and fire."

Adding the word magic into theory nets you...

Magic Background on the other hand is the key events, information, and effects that relate to magic. As an example, computer background would cover key events in the past that relate to computers today along with things like all the keyboard shortcuts and a few little 'tweaks' to make things run a little faster. It is focused on useable knowledge of the near past and today, unlike theory which is focused on future possibilities and core principles. It is a 'jack of all' skill, as long as things relate to how magic works and key events in its past. Pretty much the magical trivia pursuit skill. If used to identify a spell, it would give a trivia identification, but would not work on unique spells that well. "The mage cast 'ball of abyssal flame'"

Magic History would be the other skill in the trilogy, which I don't have to go into since everyone knows what history is.

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To help, we will use Engine Theory, Engine Background, and Engine History in a quick example.

-You would use Engine Theory as an assisting knowledge if you were: Designing a new engine
-You would use Engine Background as an assisting knowledge if you were: Modifying an existing engine for location or performance
-You would use Engine History as an assisting knowledge if you were: Trying to fix an engine and only had access to old (junkyard) parts "The LE7 uses the same crank as the old LJ4, so we can use that one"

Magic Background is general knowledge on the subject of all things magical. It covers anything and everything magical, but only in generalities. Specific topics are covered by specific knowledge skills such as Magic Theory, Spirit Lore, and so on and so forth. It's up to the GM to set proper difficulties and give proper information based upon which skill is being used, just like any other knowledge skill.

Using Computer Background as InfinityzeN pointed out, everyone with that skill would know the basics. They'd know UNIVAC was one of the first computers, they'd know who Bill Gates was, they'd know what a PCI slot was, they'd know how many kilobytes were in a megabyte, and they'd probably even know a little BASIC or other programming language -- or at least identify it if they saw it. They wouldn't be very likely to tell you how a motherboard works or how "Hi, My Name is Blank" translates into Binary. That's covered by more specific knowledge skills such as Electronic Engineering and Machine Languages. They should, however, have a chance to know that, hence the higher degree of difficulty for the guy with Computer Background vs. those other skills.

Magic Background is the same way.