I read a description of these genres once in one of the fantasy or science fiction magazines. I wish I could remember which one. It might have been Asimov’s, in which case it probably would have been written by Norman Spinrad.
Whoever wrote said that it all fits in the realm of speculative fiction. Strictly speaking, he wrote, science fiction is a subgenre of fantasy. Fantasy is all the things we can think of that are not currently possible. Science fiction are the things that are not possible but that must be scientifically plausible.
One rule I read said that hard science fiction was allowed to break one rule of physics (say time travel). The more rules of physics you break, the more you get into the realm of pure fantasy, but it is all fantasy. Just some of it seems more possible than other parts of it.
If you break no laws of physics, then I guess it is considered ordinary fiction. Although a lot of that is speculative, if it happens in the near future. But you can also have speculation about things that happened in the past, so you get historical fiction or alternate historical fiction, which is considered part of science fiction.
There are so many subgenres to all this it isn’t funny. I’ve written enough for the moment.