In brief
font-style distinguishes normal, italic and oblique faces. italic generally requests a specifically designed italic face, while oblique requests a slanted form.
Useful to know
font-style distinguishes normal, italic and oblique faces. italic generally requests a specifically designed italic face, while oblique requests a slanted form. [1]
The distinction matters in extended text. Do not judge by the slope of one letter alone; inspect the family's faces and Bulgarian characters. Styling does not itself add semantic emphasis to HTML.
Sources
For further detail and to check the information: