What do Online and Offline mean in Viber? If my bf's viber shows he's online and then in the middle of the night it changes to offline, what does this mean? Does it mean that when he's at home and within reach of the internet it shows him to be online if his Viber app is active? And does it mean that he has gone out of range of the internet if his Viber states he's offline? (He has a Samsung Galaxy Fame.)
"Online" means that Viber is running in the foreground or background (the user is available for calls or messages). When the phone has no internet connection, or the user manually used the "Exit" option inside Viber, this changes their status to "Last online at..."

In some cases, depending on the mobile kernel and software, the user uses something like Power Saving Mode, so after the idle time, the Wifi is turned off or some background application is turn off ... so Viber is turned off, your bf's viber state is also offline.