Harders
"Harders" is the plural form of "harder," which itself is a comparative adjective. "Harder" means "more hard" or "more difficult." Therefore, "harders" can refer to multiple things, people, or tasks that are more difficult or require more effort than others.
The term doesn't typically function as a proper noun or a standalone subject of encyclopedic discussion. Its meaning is entirely dependent on the context in which it is used.