any disorder that affects verbal or written communication. 

A speech disorder is one that affects the production of speech, potentially including such problems as poor audibility or intelligibility; unpleasant tonal quality; unusual, distorted, or abnormally effortful sound production; lack of conventional rhythm and stress; and inappropriateness in terms of age or physical or mental development. A language disorder is one that affects the expression or reception (comprehension) of ideas and feelings, potentially including such problems as reduced vocabulary, omissions of articles and modifiers, understanding of nouns but not verbs, difficulties following oral instructions, and syntactical errors. Although speech disorders and language disorders are two distinct entities, they often occur together and thus generally are referred to together.