When one has difficulty understanding (i.e. receptive language) or sharing thoughts, ideas, and feelings (expressive language), then they have a language disorder. A language disorder may involve difficulty in grammar, vocabulary, and/or the social use of language. It may be developmental (as is the case with most children) or acquired.
A neurologically acquired language disorder is referred to as aphasia. Acquired language disorders result from damage to the left-hemisphere of the brain, usually following a stroke or brain injury. An individual with aphasia may have problems with speaking, listening, reading, and/or writing.
Below is a table of typical infant/toddler language development (table courtesy: American Speech & Hearing Association)