HDR (high dynamic range) gives images high contrast, making bright things brighter and dark things darker. It makes photos and videos look more stunning. Support for HDR in videos is much like 4K though as it requires both the content and the hardware to make it work.
Sony is working on the hardware part. They’ve announced a firmware update will come to their Android TV powered TVs this fall to support HDR.
Looking for HDR content on your Sony TV? Try the Amazon Video app. Episodes of Transparent and Mozart in the Jungle are encoded with HDR and should be good starting places for users once this update is released.