The MC is called Himura Kenshin. And Kenshin is a name given to him (meaning "heart of the sword", or something similar). But I can't remember "rurouni" ever being mentioned whatsoever in the series? I know "rurounin" means wanderer, and "rurou" has a similar meaning (e.g. vagrant). But looking it up to confirm it, the title is literally "rurouni" kenshin. So what the hell is "rurouni"? Why is it named that way?
According to the Rurouni Kenshin Fandom wiki page:
Rurouni (るろうに), while being a word invented by Rurouni Kenshin author Nobuhiro Watsuki, has a meaning similar or identical to that of the word rōnin (浪人), which refers to wandering, masterless samurai.
"Rurouni" is often being seen translated into "wanderer", which is not a real Japanese word. The show is also often dubbed as "Wandering Samurai" or "Wandering Swordsman."