Character status refers to the availability of a character via online download through an official source, most often via the author's website.
Generally, it is divided into four different statuses: online, offline, private and trade.
Note that the status of a character may change through its lifetime, and some characters may be online for a very short period of time.
Characters whose status is online are available through an official source, most often the author's website or an official forum release. They can be downloaded freely (or at least, with free registration) and used in M.U.G.E.N.
Most M.U.G.E.N characters listed on this database are online, as evidenced by the availability of an external link.
Characters whose status is offline were formerly available through an official source, but for one reason or another, the author has decided to cease offering the character through that official source.
Occassionally, this may also occur when a hosting service for an official channel goes down, preventing further downloads of a character.
These characters can be very difficult to get for M.U.G.E.N, though warehousing can allow someone to attain the character even after it has been taken offline.
Particularly rare offline characters can only be attained through email swaps from those lucky enough to have downloaded them while they were still online, and thus are usually good for folder trading.
As the name suggests, characters whose status is private are not intended for public release.
These characters are usually edits of regular characters in one way or another, and may be kept private in pursuit of exclusivity (especially for those who upload Watch Mode battles) or due to the edit not being a significant change from the original character.
It is a common practice by some creators to keep characters private while in their beta stages, only allowing a handful of people to download them for testing purposes, then making it a public release after the character is complete. Some creators also keep characters inside full games private, only publicly releasing them some time after the release of the full game. This is a regular practice by the Infinity Mugen Team, who release their characters in "release parties" after their full game releases.
Do check with the associated individual if a character is private before asking for it - requests for private characters are almost always rejected, and frustrate both parties to no end. However, certain authors will gladly trade their private characters or release them for beta testing.
Trade characters are characters mainly ment to be used as trade pieces to get other characters, such as the case of many orochi edits, trade characters are, overall, less private but still not public characters.