For example, this game on Kickstarter (which doesn't seem to have a Player Count).
Image Source: BGG
5E means Dungeons & Dragons 5th Edition.
So when you see this on KS, it means it's a module for RPG stuff compatible with Dungeons & Dragons 5th Edition rules. There is no player count because it's an RPG, so it doesn't really apply.
I like that because whenever I see 5E on a cool looking picture I know I can pass without question.
So 5E is kinda generic? A 5E expansion could work with many different DnD 5th Edition games? What's a good example of such a game?
@Cadet Stimpy D&D 5th Edition is, basically, a set of rules, that I think are mostly covered in the Player's Handbook and the Dungeon Master Handbook. Then you have plenty of other official books (the Monster Manual, scenario books, books with specific settings, additional pieces of lore, etc.).
Now with the rules, you can set up an adventure in any setting, it doesn't have to come from an official book. Usually, the stuff that appears on KS is that: new settings (depictions of specific places, of enemies, with their stats, possible maps of locations, etc.) and new scenarios. But then you must rely on the D&D rules to play them.
It's a bit like Warhammer figurines: you have a core ruleset, but then you can play with any minis provided they have stats compatible with that core ruleset.
Note that I have never played D&D nor Warhammer so... I am not the most reliable source of info here.