DSR stands for Dynamic Super Resolution. This featured was introduced 2 years ago.

When being turned on, the graphics card will renders a game at higher resolution and downsampling to the lower resolution(s) for output. This way, the images of the game will look sharp and clean and no jiggles without relying on any anti-aliasing techniques.

Let's say the game is rendering at 4K resolution and downsampled to Full HD resolution for example.

Of course there's a weakness on DSR or any downsampling techs; You would need a powerful graphics card as rendering game at resolution that is higher than your monitor's maximum resolution requires more graphics processing power.