From their 1Q 10Q (2Q is not up yet): . We define a monthly active user as a registered Facebook user who logged in and visited Facebook through our website or

From their 1Q 10Q (2Q is not up yet): . We define a monthly 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), in the last 30 days as of the date of measurement. MAUs are a measure of the size of our global active user community on Facebook.