Abbreviations deriving from Latin terms and phrases can be troublesome for us non-Latin speakers. Here’s the long and short of the most common short forms adopted into English from the classical language:
This abbreviation of exempli gratia (“for example”) is not only often left bereft of its periods (or styled eg.), it’s also frequently confused for a similar abbreviation you’ll find below. Use e.g. (followed by a comma) to signal sample examples.
This sloppily formed abbreviation of et cetera (“and so forth”) is often misspelled ect., perhaps because we’re accustomed to words in which c precedes t, but not vice versa. (Curiously, Merriam-Webster spells out etcetera as such as a noun, but at the end of an incomplete list, retain the two-word form, or translate it.) A comma should precede it.
Refrain from using etc. in an e.g. list; the abbreviations are essentially redundant, and note that etc. is also redundant in a phrase that includes including.
3. et al.
This abbreviation of et alia (“and others”), used almost exclusively to substitute for the names of all but the primary author in a reference to a multiauthor publication or article but occasionally applied in other contexts, should have no period after et, because that word in particular is not an abbreviation.
Also, unlike as in the case of etc., refrain from preceding it with a comma, presumably because only one name precedes it. Fun fact: We use a form of the second word in this term — alias — to mean “otherwise known as” (adverb) or “an assumed name” (noun).
This abbreviation of id est (“that is”) is, like e.g., is frequently erroneously styled without periods (or as ie.). It, followed by a comma, precedes a clarification, as opposed to examples, which e.g. serves to introduce.
This abbreviation of flourit (“flourished”) is used in association with a reference to a person’s heyday, often in lieu of a range of years denoting the person’s life span.
This abbreviation for nota bene (“note well”), easily replaced by the imperative note, is usually styled with uppercase letters and followed by a colon.
7. per cent.
This British English abbreviation of per centum (“for each one hundred”) is now often (and in the United States always) spelled percent, as one word and without the period.
This abbreviation, short for in re (“in the matter of”) and often followed by a colon, is often assumed to be an abbreviation for reply, especially in email message headers.
This abbreviation of videlicet (“namely”), unlike e.g., precedes an appositive list — one preceded by a reference to a class that the list completely constitutes: “Each symbol represents one of the four elements, viz. earth, air, fire, and water.” Note the absence of a following comma.
This abbreviation of versus (“against”) is further abbreviated to v. in legal usage. Otherwise, the word is usually spelled out except in informal writing or in a jocular play on names of boxing or wrestling matches or titles of schlocky science fiction movies. (“In this title bout of Greed vs. Honesty, the underdog never stood a chance.”)