"Unread notifications" refers to messages or alerts that have not been opened or seen by someone on their device or platform.
Sentences with «unread notifications»
(Other Windows Store apps also display the number of unread notifications stashed in the taskbar.) (pcworld.com)
With the next Android Wear update, 2.9, all watch faces will show an indicator for unread notifications. (androidcentral.com)
Basically, this puts a small badge on top of the app's icon that specifies how many unread notifications you have (much like iOS does by default). (howtogeek.com)