Slanted type like this, with a number of distinct uses.
Used in these posts to set off a word or phrase that is being discussed. Quotation marks would serve that purpose just as well, although things might look a bit cluttered and fussy.
More commonly, italics are used for emphasis. Go easy with emphasis of any kind: if everything is emphasised, the force is diminished.
In the old days of manual typewriters with only roman (non-italic) typeface, underlining stood in for italics. Underlining can still be used, especially where you’re quoting something that already contains italics but want to add your own editorial emphasis (indicate that in square brackets with something like underlining mine or underlining added).
Italics are also used to indicate foreign expressions. In these, the law abounds: ultra vires, sine die, cy-près, autrefois acquit, to mention but a few.
Two observations, though. First, you’re better off not (or perhaps that should be not) using dead languages at all if there is a good English equivalent. Secondly, after a certain point, foreign words and phrases become fully part of English and lose their italics. We don’t write etc.; it’s now naturalised and needs no italics.
In literary writing, there is a new movement to drop the italics for any ‘foreign’ word or expression, on the grounds that differentiating typefaces creates ‘a monolinguistic culture of othering’ that presupposes the primacy of English and fails to reflect the experience of bilingual and multilingual people: https://quartzy.qz.com/1310228/bilingual-authors-are-challenging-the-practice-of-italicizing-non-english-words/. That has yet to hit the law, however.
A final legal use of italics is in styles of cause, aka case names. Traditionally, these were rendered like this: Hadley v. Baxendale. The v for versus is NOT in italics because when you italicise something containing an element that already has italics, you convert that element to roman type. Because switching back and forth between typefaces was a bit of a pain, we now italicise everything and also drop the period after the v (both to the horror of traditionalists). By the bye, the traditional way to refer in speech to a case is Hadley AND Baxendale, not Hadley VEE Baxendale or even Hadley VERSUS Baxendale.