What does the white check mark on Facebook messenger mean?

[Anonymous]

I sent message almost a week ago. He's been online... We're just friends, so I know he didn't block me. Any other explanation as to why he just quit talking to me? I don't have his number 😩

[theKris94]

It is sent, but not received yet.
It might not have been received yet because either the person's app haven't been opened yet (and notifications have been turned off). Or Messenger is experiencing some server issues that makes it impossible to forward the message at the moment.

[CyberWarrior98]

Means you sent the message. That it is delivered to the person you sent it to.