Articulation refers to the production of speech sounds. An articulation disorder occurs when children produce errors in individual speech sounds. These errors can be distortions of a sound or a substitution of a sound (e.g. /f/ for “th”) Other forms of speech sound errors are phonological errors which are patterns of errors that affect more than one sound (e.g. leaving the final consonant sound off of words). These error patterns are used by children to simplify their speech when learning to talk, but they are expected to be eliminated by certain ages. Children with articulation or phonological disorders may be difficult to understand to unfamiliar listeners.