On brain mri what does "mild to moderate deep white matter flair hyperintensity burden" mean? what would cause be?

Complex question: Why did u get an MRI? FLAIR is "fluid attenuation by inversion recovery," 1 of many ways that MRI signals r obtained. Hyperintensity means the signal was stronger than expected. I suspect this is an artifact of MRI, unrecognized by the radiologist. If you are feeling no different than before, & if you have no symptoms, I wouldn't worry too much. http://www.actaneurocomms.org/content/1/1/14