a shape that you cannot see clearly, often because it is moving too fast

something that you cannot remember clearly

The events of that day were just a blur.

if the shape or outline of something blurs, or if something blurs it, it becomes less clear and sharp

if something blurs your eyes or vision, or your eyes or vision blur, you cannot see things clearly

to become or make it become difficult to recognize a clear difference between things 

The differences between art and life seem to have blurred.

The line between make-believe and reality became increasingly blurred.

She tends to blur the distinction between her friends and her colleagues.

His work has blurred the boundaries between children’s and adults’ fiction.

LEARNit Dictionary