A stroke was the rapid loss of brain function due to disturbance in the blood supply to the brain.
Aphasia was one of the results of a stroke. (DS9: "Babel")
In 2372, The Doctor searched for evidence of a stroke as one of several potential explanations for Captain Janeway's hallucinations. (VOY: "Persistence of Vision")
Later that year, Joseph Sisko suffered a mild stroke brought on by his atherosclerosis, but made a good recovery. (DS9: "Homefront")
In 2373, Grand Nagus Zek almost had a stroke when he discovered that Ishka, with whom he had been corresponding, was a female and Quark's mother. (DS9: "Ferengi Love Songs")