A file sharing site is any site that you can upload files to, usually in order to share them with others. This usually involves some sort of count down timer delay before you can download the file, unless you pay for a premium account, in which case you can bypass the timer, and sometimes download the file directly without a landing page.
/rs/ was a board on 4chan that displayed all of the filesharing downloads that were posted on any thread on 4chan. The archive was never reset and had many years of interesting information, even if many of the downloads were dead due to the take down of MegaUpload and files expiring on RapidShare.
Unfortunately, that faggot moot took /rs/ down and all of that interesting data is now gone, forever.
MediaFire is a file sharing site that came in shortly after MegaUpload and allowed large download quotas and large file uploads. MediaFire became very active in responding to DMCA requests, rendering their service pretty much useless for most of the files that 4chan would have wanted to share.
Megaupload was a file sharing site that some fat fuck scammer names Kim Dotcom was running. His company would make deals with skids, allowing them to pay to keep their illegal files from being removed by DMCA requests. The DoJ and FBI raped the Megaupload servers with the help of the police service of the country they were hosted in. The fat fuck is still running away from the USA because if the DoJ and FBI could get their hands on him, they'd rape him with a pineapple.
Due to the idiocy of 4chan's users, a huge amount of 4chan-related files were only uploaded to Megaupload. This pretty much killed the ability to download any files from a three year period between people using RapidShare and Megaupload's servers being raped.
MegaConz / Mega
The fat fuck Kim Dotcom eventually opened a new site called Mega. The site supposedly encrypts every file uploaded to it. The outcome of the retard's idiotic idea created a site that's just a broken piece of shit that doesn't work the majority of the time.
Due to the fat fucker's choice of domain, mega.co.nz, people would just call the site MegaConz. The name is very fitting when you consider that Kim Schmitz, aka Kim Dotcom, is a conman, a scammer, and a thief.
RapidShit is the nickname for the file hosting site RapidShare. RapidShare is the first massive and well known file sharing site, originally using the domain rapidshare.de.
rapidshare.de ended up ass ramming every paid customer by shutting down without notice around the time when many competent competitors started appearing. All of RapidShare's competition provided better services, by far, so it's no surprise that they decided to steal hundreds of thousands of dollars to stay afloat.
At the same time that rapidshare.de temporarily went offline, a "new" site using rapidshare.com appeared; it was just as shit. After rapidshare.de went back online, RapidShare started pretending that the two sites weren't affiliated in order to prevent people who paid for a premium account on rapidshare.de from being able to carry their accounts over to rapidshare.com.