Final answer:
Aphasia is the lack or impairment of the ability to form or understand speech. It is a language disorder that can result from damage to the brain. Different types of aphasia involve different aspects of language processing and production.
Step-by-step explanation:
The lack or impairment of the ability to form or understand speech is aphasia. Aphasia is a language disorder that can result from damage to the brain, typically the left hemisphere. It can affect a person's ability to produce or understand spoken or written language. There are different types of aphasia, such as receptive aphasia and conduction aphasia, which involve different aspects of language processing and production. A common cause of aphasia is a stroke, but it can also be caused by other brain injuries or diseases.