"The idea behind both of these new emerging (and currently illiquid) markets is to provide a place for private equity investors to trade securities with each other. The companies remain private, do not have to file with the SEC, and do not trade daily like public stocks do. When an entrepreneur or investor wants liquidity on a position they own, they come to these private markets, offer their position or part of their position for sale, and a trade is made."
Basically, it's a market where investors that own shares in private companies can get cash for those shares from other private investors without taking their company public and being subject to all the bureaucratic rules that apply to public companies.
In theory, you could also do this by simply trying to find an outside investor yourself, but the hope is that by creating a market, it will be a more efficient process.
er... can I get a translation?
...I'm not sure my positions are liquidy enough.