Apico-dental refers to sounds produced by the contact between the tip of the tongue and the upper front teeth. Synonyms for apico-dental include "interdental," which refers to sounds made by pushing the tip of the tongue between the upper and lower front teeth, and "lamino-dental," which refers to sounds produced by the tip of the tongue touching the backs of the upper front teeth. Other related terms include "dental," which refers to sounds produced by the tongue touching the teeth in general, and "labiodental," which refers to sounds produced by the lower lip touching the upper front teeth. These different terms are important for understanding the distinctions between various speech sounds in different languages and dialects.