[rcxdude]

That's a monthly active user. A daily active user would be someone who logged into an account in the last day. Generally monthly active user count will be higher than daily active users, but for something like Facebook the difference is about 50% (which is what the second article linked is explaining, if you read more than just cherry-picking a line that matches your preconceptions)

And yes, that's a claim that if each user is a separate person, >20% of the world's population interacts with Facebook at least minimally each day. You can add your own interpretation about how many of the accounts are bots or otherwise duplicates, but it's a staggering amount either way.