失语症（英语：aphasia，源于希腊语、aphatos：意指无法说话、又称为 rhymnasia）。症状是由于特定脑区损伤而丧失产生语言或了解语言之能力；发音功能属正常，但不能说出有意义的语言。失语症是由特定脑区受损引起的语言障碍，这些特定脑区包含管理语言产生的布若卡氏区（Broca's area），或管理语言理解的的韦尼克区。但失语症并不属于感觉（sensory）、智力（intellectual）、或精神疾病（psychiatric）上的缺陷，或是肌肉无力及认知失调。

仔细查看受伤之脑区，某些失语症患者或许能够说话，但无法书写，反之亦然。也可能由各种语言障碍方式表现，例如能够唱歌，却无法说话。失语症可能与随着其他脑部损伤疾病共同并发，比如{[le|构音障碍|Dysarthria}}，这是因言语使用之肌肉功能失调而造成之语言丧失症；或表达障碍，意指无法正确或连续地以口说的方式使用语言。

Aphasia is a combination of a speech and language disorder caused by damage to the brain that affects about one million individuals within the US. Most often caused by a cerebral vascular accident (CVA), which is also known as a stroke, aphasia can cause impairments in speech and language modalities. To be diagnosed with aphasia, a person's speech or language must be significantly impaired in one (or several) of the four communication modalities following acquired brain injury or have significant decline over a short time period (progressive aphasia). The four communication modalities are auditory comprehension, verbal expression, reading and writing, and functional communication.