What are the differences between the two? Is italic simply a character that's been tilted using software, and oblique is one that is drawn as a slanted character from the get go?
If anything I/d see it more the other way round-italic is a cursive typeface, usually angled and with some of the aspects oh handwriting in it's letterforms. Oblique is more usually just an angled form of a regujlar face-though this may be done by hand rather than in software, and may go beyond just a mechanistic tilting.
Generically/commonly one could call them synonyms.
Historically (and probably more accurately) italics is an actual separately drawn typeface meant to hint at aspects of cursive handwriting. The glyphs are drawn as unique glyphs from those drawn for the text face (though are meant to feel like they come from the same family in terms of size and style and weight).
Oblique, on the other hand, is usually more of a mechanical slanting of the standard glyphs rather than a re-drawing of the glyphs.
There's also the issue outside of the typeface itself when it comes to the wordprocessor. Smart wordprocessing software, when you click the italics style icon will swap out the current typeface for the italics version of the typeface. If there is no italics version, it will take the standard text face and distort it (obliquing it [is obliquing a verb?]).
This is a very clear explanation on the differnence between italic and cursive and also has some other usefull lessons on typedesign. http://www.typeworkshop.com/index.php?id1=type-basics&id2=&id3=&id4=&id5...
Nothing earthshaking, but:
In preparing my TypeCon talk I had to think clearly about definitions like this, and what I arrived at is close to what some others have already said:
Oblique is a mechanical skew of a Roman, possibly touched up (not more) to avoid too much ugliness. Sans fonts often have an Oblique (although they call them "Italic" for convenience/expectation) and these only stand out enough from the Roman if they have a strong slant.
Italic means a font that might have started as a mechanical slant job, but in any case ends up looking structurally different. Serif fonts almost always have a so-called "true" Italic (although also almost always the Italic skews the voice of the Roman too much, typically by being far more chirographic). Slanted-Roman italics are interesting because they are essentially Oblique, but they [need to] have something extra (like semi-serifs instead of full serifs) to stand out enough.