The abbreviation threw me off at first, I'll admit—thought it might be some new genre tag for ethereal fantasy or something. Turns out it's just academic shorthand, Latin for "and others." You see it on research papers and scholarly books all the time, but the key difference from, say, a multi-author anthology or a novel written by two people is how it signals the primary contributor. The first name listed is usually the lead researcher or principal author, the one who did the bulk of the writing and organizing, while 'et al.' politely nods to the rest of the team.
It creates this weird hierarchy on the spine. With something like 'Good Omens' you've got Pratchett and Gaiman right there as equals. An et al. credit feels more like a project report, where the collective effort is acknowledged but the individual gets top billing. I find it changes how I approach the book, too—I'm more likely to attribute the core thesis and any flaws to that lead author, whereas with a true collaboration I think about how the voices blended or clashed.
Honestly, outside of academia and some dense nonfiction, you don't see it much. It's less a creative partnership and more a documentation of a group endeavor, which is fine, but it lacks the romance of a co-written novel. You're not wondering who wrote which chapter; you're assuming the first author steered the ship and the others handled specific data or sections.
To end, I just skimmed a sociology text that used it, and the citation style almost feels like a legal formality rather than a celebration of joint work.