white matter usually refers to the deeper tissues of the brain subcortical, which contain nerve fibers. Those fibers are surrounded by myelin, the covering of the nerve fibers. Myelin gives the white matter its color. Lesions are usually abnormalities that are found in the white matter. I found this really great article that does a deep dive in white matter lesions, giving much more context to what white matter is in general and the abnormalities that can exist within it. https://www.brainandlife.org/articles/what-are-white-matter-lesions-are-they-a-problem#:~:text=Abnormalities%20in%20white%20matter%2C%20known,matter%20deteriorates%20as%20people%20age. My apologies for the long URL. I hope this helps to answer your question. Kayleigh, MultipleSclerosis.net team