In No Man's Sky, the seemingly infinite exploration game developed by Hello Games, the line between single and multiplayer is kind of blurry. The universe in which you'll play is shared with other players online but since space is so incomprehensibly huge the chances of you actually running into your friends when playing is quite small.
So small, in fact, that Sony and Hello Games themselves seem to think of No Man's Sky as a single-player experience. And as such the game won't require a PS Plus membership to be played, though you'll have to be connected to the internet for your discoveries to be properly saved to the universal atlas, as confirmed by Gameinformer.
So if you don't want to pay up for PS Plus but still want to play No Man's Sky on Playstation 4, you're covered.