semantics like this are a pain in every trade/craft/hobby/etc... It's always educated participants in the craft or hobby that understand what the words are trying to convey VS marketing that uses whatever descriptions they want and incorrectly educating the general public who has no other primary source of information (lets be real, most people aren't gonna do huge amounts of research when buying something other than reading the marketing crap).

The unique issue with these semantics in the leather world is that, from what I can tell, almost every single term commonly used was coined by marketers.

My general rules of thumb:

1. if a product has any kind of stamp on it denoting what kind of leather it is, run. The only producers/companies that need to prove what kind of leather they are using via a stamp are the ones that are likely trying to pull one over on you. The terms aren't regulated (that I know of?), people can put whatever they want on things. There might be some "full grain" stamps out there that are accurate, but I'd be skeptical if I saw them.
2. "Full Grain": the good shit. The smooth side hasn't been messed with aside from maybe some dye and finish. No sanding, no weird crap to make it look more uniform than it is (light embossing doesn't count so far as I'm concerned, feel free to change my view). I know that technically patterned/embossed leather doesn't count, but if we are using these terms to differentiate between qualities of leather, then there is no reason a lightly embossed leather is inferior to a true "Full Grain".
3. "Top Grain": technically, if your leather was ever split, even at the tannery, its top grain. There's nothing inherently wrong with it. Its less of a marker of quality, and more of a "right tool for the right job" distinction. As long as the smooth side wasn't messed with, its good to go. You wouldn't want a full grain cowhide wallet, that would suck.
4. "Nubuck": top grain or full grain leather that's had the smooth side sanded and messed with to rough-up and expose fibers. This is still "right tool for the right job" kind of thing, but now structural integrity has been lowered enough that you probably should not use this leather for anything that needs tensile strength. The smooth side is, proportionally, where most of the strength comes from. Once it's been broken up and messed with, you start to compromise integrity. Nubuck is, however, pretty good at not showing wear, making it a good choice for shoes or anything else that gets throw around a lot but doesn't technically require a ton of tensile strength anywhere.
5. "Suede": getting close to the danger zone. Suede can be nubuck, or it can be splits that have been finished. Never trust a "suede" product unless its from a well known manufacturer of quality goods. Even then, durability will usually not be as good as other types.
6. pretty much everything else can be classified by one of the above, plus maybe some outliers that span two categories. The problem is that companies make up their own semantics to define these "other" leathers a lot of the time rather than just making a cool name and including a byline: e.g. "Company X Badass Leather: this is a full grain leather that's been messed with in Y way."