The voiced dental fricative is a type of consonantal sound, used in some spoken languages. It is familiar to English speakers as the th sound in father. The symbol in the International Phonetic Alphabet that represents this sound is eth, or . This was taken from the Old English letter eth, which could stand for either a voiced or unvoiced interdental non-sibilant fricative. This symbol is also sometimes used to represent the dental approximant, a similar sound not known to contrast with a dental non-sibilant fricative in any language, though that is more clearly written with the lowering diacritic, . The dental non-sibilant fricatives are often called "interdental" because they are often produced with the tongue between the upper and lower teeth, and not just against the back of the upper teeth, as they are with other dental consonants.