This is an idea from the 1% rule of Internet. 1% rule says that there are only 1% of the total users contribute content to the Internet, while the rest of 99% of users are just watching and reading. According to such rule, it is possible to trace some million of users to get a whole view of the Intenet. Those million of users are the keys. As millions of users are much smaller than billions of users over the Internet.

Oh, it's just the idea of million-key-users.