Its difficult to elaborate on as the system is fairly deep and broad because its expanded upon over a large body of works by what is essentially "Japanese Marvel Comics" in terms of having a large shared universe with a bunch of semi-interacting characters.
Following the entry for Magic, Magecraft is the ability to reproduce what cannot be scientifically realized regardless of time and funds. The limits of Magecraft have changed with time, as science evolved and sorceries from before became technically possible through science. However, modern Magecraft remains far inferior from that of the past, so much that someone like Medea, who comes from the Age of Gods when Magecraft was much more powerful, would seem like a sorcerer to the eyes of a modern magus, even though what she can do is not really Magic.
Here's the entry for Magic
, so you have "magecraft" and then you have "magic", and "magecraft" is what 'magi' actually use/do but have gotten weaker overtime. All magi seem to want to access the "Root" (Akasha I think) in order to access 'magic'. A lot of magi turn themselves into vampires through magical means in order to live longer for this reason.
In gross oversimplification, "magic" can be differentiated from "magecraft" in that the consequences of its use are ostensibly "impossible" or "miraculous." Where magecraft is discouraged by the counter forces for its violation of natural processes, its end output is not inherently beyond the dictates of the world; ergo, a spell that creates a fire is not "magic," because something as mundane as lighting a match can yield the same effect. Likewise, though the Mystic Eyes of Death Perception cannot be replicated through magecraft, its use results merely in the imposition of "death" — a concept well within the realm of the "possible," and thus outside the domain of the "miraculous." By corollary, it is probable that the achievements of magecraft may be someday replicated through science, as both operate within the laws of nature.
Department of Vague Vagueness to the rescue...
For example, the most powerful magic spell in the setting comes in two forms; Marble Phantasm and a Reality Marble, because magic has various rules and the two spells each in their own way "breaks" the rules but at great cost.
Spell casting in nasuverse works like you are trying to find a particular marble, like say a white marble from a bag of a 100 black marbles. (This is not to say that magic is probablistic, its conceptual; semantics matter a lot)
The Marble Phantasm is akin to making the chance of grabbing a white marble 100% each time.
A Reality Marble is what happens when you turn all the marbles white.
Both manipulate reality itself to some degree, for example Acruid uses a Marble Phantasm to disintigrate the vampire Roa down to his feet. Reality Marbles are more about projecting your inner "world" onto reality itself.
For instance there's three particular usages of a Reality Marble that I know of (there's a fourth but I don't understand what it did).
-Alexander The Great's 'Ionian Heteroi':[/quote]
It is a Reality Marble that embodies Alexander the Great's dreams and philosophies as a king and the bond formed with his subjects. Like how Saber's Excalibur can be called the physical actualization of her ideals as a king, Ionioi Hetairoi is the actualization of Alexander's commanding abilities and his kingship.
The point is that Iskandar's Reality Marble required extraordinary historical circumstances to allow as his Noble Phantasm.
Then we have Shirou's [url=http://typemoon.wikia.com/wiki/Unlimited_Blade_Works]'Unlimited Blade Works'
Emiya does not have a true Noble Phantasm that is the crystallized embodiment of a hero's existence like many demonic or holy swords, but if a Noble Phantasm is considered to be a symbol of the Heroic Spirit, then the Reality Marble is his Noble Phantasm. It is high-class thaumaturgy that embodies their internal worlds and imprints them upon the world as a bounded field. It is their one true specialization of magecraft, the result of "Sword" being both their Origin and their Elemental Affinity, and the basis of their projection and reinforcement skills. It is the definite answer obtained by someone whose life was saved by a sword, actually merged and lived with a sword, and acted as a sword all of his life. Emiya has no penalties from the world while utilizing his version of Unlimited Blade Works.
Shirou's however slowly kills him through the backblast of it since its far beyond his level to adequately control. Each time Shirou gets harmed when using his prana his wounds get knitted back together with swords, so if he has to deploy the Reality Marble in a full on fight to the death he's likely to die shortly afterwards.
Its one of the few systems I've seen to keep Science readily in focus as "hey this is useful too!"