As others have pointed out, the ranger can be a few different things. I think the class started out as a mix of a few related things, but grew out of control. It actually a good poster child for why I've become even more disenchanted by a class-based system -- I think it's stupid to use classes as bundles of abilities without archetypes, but I've found myself doing so more and more. Since the question makes no sense unless you're talking archetype, I'll go with that train of thought.
A ranger exists between civilization and the wilds. They could be tribesmen, but not in the "noble savage" mold. That's the realm of the barbarian (which is a dumb class, but that's another thread). The ranger is a (mostly) civilized person who lives apart, not a wildling who can carry on a conversation on philosophy. They have a bit of a special forces vibe, but not in sense of being able to kick the crap out of anything better than a fighter. They're harder to kill than most, but not in the raw physicality of the barbarian. They rely on training, but not in the same way as the rogue. They're just "smarter" in the sense of being more prepared for anything that comes their way. How, exactly, does one stat up a Boy Scout without making the player actually know all the things a Boy Scout would know? Well, in five editions, we've had five different answers. But, that's the kernal of the class -- a well prepared warrior who is comfortable without comforts, thinks ahead, and knows a smattering of things that reflect that preparedness.
What isn't a ranger?
A ranger isn't a druidic paladin. Their spells are tricks and tools they've picked up, not stuff they get from their religion. This is one thing 1E got more right than any other edition. Rangers had access to both magic-user (wizard) and druid spells. They actually had more wizard spells than druid, which always made it seem like the druid spells were tacked on or were a way to create a custom spell list without actually creating a custom spell list (paladins cast from the cleric list). So, the lack of explicit arcane/divine categories in 5E works well for rangers, who really should be considered arcane casters, more than divine. Rangers don't (have to) worship nature. They're actually much, much more likely to worship the gods of civilization.
A ranger isn't death on wheels. They should lose in a straight-up brawl against a fighter of the same level (Aragorn was not the same level as most folks). But, they also shouldn't typically allow themselves to get into a fair fight. But the not fair fight of a ranger looks a lot different than the not fair fight of a rogue. The ranger is going to use cover, movement, traps and snares, hazards, etc. to their advantage. Rogues will tell you they're fighting fair then use a hidden dagger on your kidney.
A ranger isn't (necessarily) a TWF master. I don't really have an issue with some rangers choosing to go this way, but it's totally orthagonal to the archetype.
A ranger isn't a wilder-rogue. There should be a noticeable difference in the way they handle problems. The rogue has become a bit too much warrior, for my taste, but that's a different topic.
A ranger isn't (necessarily) an animal handler. Yeah, I can see it as an option, but it's not core to the archetype of being prepared.