What does that mean?
Why did they use the word "accessed" vs "authenticated"? Did the user leave a tab on their cell phone open after they logged into facebook?
Many users log in once and forget to logout... Does that continue to present itself as someone accessing facebook?
How many users access via the app? via the mobile web page?
If you take out people who used Messenger app what would this number be? Also, can I be a Messenger user and not a registered Facebook user?
Pay attention to the footnotes. It shows up on many pages of the presentation.
I would prefer knowing how many logged in each day. How many did something purposefully like look at a friends timeline, search a friend, look at possible friends. How many posted a comment, did a "like", clicked on an ad...
"The numbers for our key metrics, our DAUs, MAUs, and average revenue per user (ARPU), do not include Instagram, WhatsApp, or Oculus users unless they would otherwise qualify as such users, respectively, based on their other activities on Facebook." -> This clarifies that they are measuring users without considering any Instagram, WhatsApp or Oculus uplift.
"We define a daily active user as a registered Facebook user who logged in and visited Facebook through our website or a mobile device, or used our Messenger application (and is also a registered Facebook user), on a given day." -> This clarifies that they only count if the login happened that day or they did a visit during that day. Not passive open tabs.
It does also have this note "For example, while user-provided data indicates a decline in usage among younger users, this age data is unreliable because a disproportionate number of our younger users register with an inaccurate age." -> This might be some of what people are experiencing. A shift in demographics to older people.
[1] https://www.sec.gov/Archives/edgar/data/1326801/000132680117...
There are some challenges in how they present the data and it is unclear what you are including in the definition of "Facebook". The report doesn't break out Instagram & WhatsApp separately. So there could be a decline on Facebook.com which is offset with increases elsewhere.
[1] https://s21.q4cdn.com/399680738/files/doc_presentations/FB-Q...