Speech

Speech, or articulation, is the process by which sounds, syllables, and words are formed when your tongue, jaw, teeth, lips, and palate alter the air stream coming from the vocal folds.

A person has an articulation or speech problem when he/she produces sounds, syllables, or words incorrectly so that listeners do not understand what is being said.

Most articulation errors fall into one of three categories- omissions (e.g., "at" for "hat"), substitutions (e.g., "thun" for "sun"), or distortions (i.e., when the sound is said inaccurately, but sounds something like the intended sound).

Articulation problems may result from physical handicaps, such as cerebral palsy, cleft palate, hearing loss, or may be related to other problems in the mouth, such as dental problems. However, most articulation problems occur in the absence of any obvious physical disability. The cause of these so-called functional articulation problems may be the faulty learning of speech sounds.

References: 

American Speech-Language Hearing Association