The word aphasia comes from the Greek word "aphatos," meaning speechless. In medical terms, it refers to a loss of ability to understand or produce language caused by brain damage, most commonly from a stroke. Aphasia can affect speaking, listening, reading, and writing in varying combinations and severities. It's classified as a language disorder, which is different from a speech disorder — the problem isn't with the muscles of the mouth or vocal cords, but with the brain's language processing system.