I see all kinds of people these days, actors even, missing the word “cameo.” My understanding of a cameo is a brief uncredited appearance by someone famous for a few seconds in a movie or TV show, like Hitchcock or Stan Lee would often do. It is not normally an actual role or a character that would appear in the credits; something like the many actors and characters like Wesley Snipes/Blade that appear in, say, “DeadPool and Wolverine” or Bruce Springsteen on Curb Your Enthusiasm would be guest appearances rather than actual cameos. Discuss.
I’m ok with any brief appearance being called a ‘cameo’, credited or not.
Weirdly, Stan Lee in the MCU is a counterexample according to your criteria, since he was usually credited as an identifiable character, not appearing as himself.
I think there are degrees between “Blink and you miss it”, short appearances with maybe one line of dialog, and extended appearances.
“Blind and you miss it” seems to be @biffster’s preferred defintion.
I personally fully include the second, such as The Rundown, where Schwarzenegger passes by and exchanges a single line to have fun (IIRC) and is uncredited, although I would still accept it if he was. The point is it’s a short appearance that has no affect on the story, but is a “gee whiz” moment for fans.
The third, I agree, isn’t a cameo, it’s a minor role. Back to the OP, Wesley Snipes’ appearance in DP&W shouldn’t be considered a cameo. They have far too much dialog and screen time, so they’re a minor role, or minor supporting actor.
A borderline case can be made either way in the example of roles such as Bruce Campbell in Raimi’s various movies including the Spiderman series. It’s generally a short bit, with a few spoken lines of dialog, and credited, but it doesn’t affect the story except in the most minor ways - it’s filler, and a favor to friends (see the various SNL actors as examples of this as well) going both ways (sometimes a famous actor will do a cameo for a friendly director or actor rather than the director doing it for someone else).
So yeah, like a lot of things, a wide range of possibilities, isn’t it fun?
Sure is! 
One of the criteria Hollywood folk use to describe some cameos is pay rate. If someone who normally warrants a big payout agrees to do a small part for scale, that’s considered a cameo.
One problem with us outsiders using this is the information on pay is often not public.
Every Stan Lee credit I’ve seen has been as “Himself”. He does have a few recurring “characters” (a billionaire playboy, a nutty professor, etc.), but none are named.
That’s what I thought as well. In fact, I think the only true cameo in the DP&W movie (apart from Stan Lee on the side of a bus) was the Henry Cavill blink and you miss it appearance as one of the Wolverines. No speaking lines and just a brief appearance.
Why should it make a difference to us outsiders? We see someone recognizable in a bit part, a part that could have gone to extra if it was included at all, that’s enough of a cameo to me. I don’t care if it’s credited or how much the actor was paid. It may add nothing to the movie aside from the appearance of a celebrity of some type.
[Moderating]
Oh, and I hadn’t noticed before that this wasn’t already in Cafe Society. Easily enough fixed.
Connecting to Ryan Reynolds, who’s a big fan of cameos, he has one in the Brad Pitt movie Bullet Train. He appeared onscreen for six seconds in exchange for Brad Pitt’s cameo in the first Deadpool that lasted the same amount.
I’d go with the definition that a single scene, like Reynolds’ appearance in Bullet Train or Chris Evans’ in Free Guy, was a cameo, while Channing Tatum’s appearance in both those films was a bit part (multiple small scenes).
Now those are what I call cameos! Brad Pitt was a real blink and you miss it moment. Channing Tatum’s appearance was definitely a character part, not a cameo. Donald Trump in Home Alone 2 would be more like a cameo. They can put them in the credits, but it kind of takes away from the fun if you ask me.
Ryan Reynolds also had a brief appearance in Harold & Kumar Go to White Castle.
They want really a cameo though because he wasn’t a big star yet.
I will quote myself, from the thread on season 3 of The Mandalorian:
“These appearances” referred to Lizzo and Jack Black playing roles in an episode of The Mandalorian. They were widely referred to in the media as “cameos,” even though if they had been played by actors you’d never heard of, no one would have called them that.
So this has been going on for awhile, and I agree that the term “cameo” is frequently misused.
It almost seems like the word “cameo” is transmogrifying through overuse into something less specific and less meaningful.
Doesn’t mention credits. small but noticeable covers a lot of ground. I don’t think the meaning has changed.
I would call Hugh Jackman’s appearance in X-Men: First Class a cameo.
Well-known, credited or uncredited. Mike Todd coined the term ‘cameo’ for “Around the World in 80 Days (1956).” Pretty sure those were all credited.
Wow, that film had a long list of cameos.