Blu-ray is an improved technology (how the disc is made) that allows for a higher resolution, which makes the picture look sharper and more detailed.

DVD is 720 × 480 pixels, BR is 1920 x 1080 pixels.

There is now UHD Blu-ray, which has a resolution of 3840 X 2160 pixels - this is known as “4K”, and is effectively 4 times to resolution of a blu-ray.

8K would notionally come next but the “winning” format is yet to emerge; different companies will try to market their own media until one is widely adopted or has market share.