Speech defects, also known as speech disorders, are conditions that affect a person's ability to produce sounds that are necessary for clear and effective communication. One of the most common speech defects is lisps, which is characterized by the mispronunciation of certain sounds, such as the substitution of 'th' for 's' or 'z' sounds. Lisps can be caused by a variety of factors, including physical abnormalities in the mouth, tongue, or throat, as well as neurological or psychological issues. Treatment for lisps typically involves speech therapy, which can help to correct the mispronunciation of sounds and improve communication skills.