What does this mean on Facebook?

[Rosalie]

I was added to a group and when people post, a little bit later it says seen by (insert number here) people. Does this mean someone clicked on it or just saw it while scrolling down?

[Pieman]

I've been added to face book groups, with out being asked, too. But I've never seen it say insert number. Maybe the group you were added to, wants you to choose a number, for the purpose of identification- in which case you're certain number of member.