In typography, italic type is a cursive typeface based on a stylized form of calligraphic handwriting. Owing to the influence from calligraphy, such typefaces often slant slightly to the right. Different glyph shapes from roman type are also usually used—another influence from calligraphy. It is distinct therefore from oblique type, in which the font is merely distorted into a slanted orientation. However, uppercase letters are often oblique type or swash capitals rather than true italics. [...]
Oblique type (or slanted, sloped) is roman type which is optically skewed, but lacking the individual letter forms and cursive accoutrements of true italics.
In many computing interfaces, the text leaning effect is called Italic, whether or not an italic font is used to render the text. The start of this confusion possibly appeared when Adrian Frutiger named the slanted versions of his typefaces Univers and Frutiger as italic. In the case of Univers, only Univers 65 Bold has an italic-named counterpart. Since then, many font families, primarily sans-serif fonts, have called the oblique fonts italic. Although updated versions of those font families begin to incorporate italic features, some font families, such as Avenir Next, Linotype Univers, Neue Helvetica, do not.
Although an oblique font can be generated by simply tilting the base font, some designers use optical correction to correct the distorted curves this introduces. Some font families have fonts with both italic and oblique variants. In these cases, the oblique font may have a different tilt angle from the italic font. For example, Univers 65 Bold Oblique has a smaller leaning angle than the Univers 66 Bold Italic. [...]
Oblique type (or slanted, sloped) is a form of type that slants slightly to the right, used in the same manner as italic type. Unlike italic type, however, it does not use different glyph shapes; it uses the same glyphs as roman type, except distorted. Oblique fonts are usually associated with sans-serif typefaces, especially with geometric faces, as opposed to humanist ones whose design tends to draw more on history. Oblique and italic type are often confused.
An example of normal (roman) and true italics text:
The same example, as oblique text:
The start of this confusion possibly appeared when Adrian Frutiger named the slanted versions of his typefaces Univers and Frutiger as italic. Following this viewpoint, sans-serif typefaces often do not have true italic versions. The Gill Sans and Goudy Sans typefaces are two well-known exceptions. The sans-serif fonts within the ClearType Font Collection introduced in Windows Vista typefaces have true italic versions, as does the older Trebuchet MS typeface.