also: ぼいんさんかくけい
noun
vowel triangle
Technical term in phonetics referring to a triangular diagram that plots vowel sounds based on tongue position.
母音三角形は、舌の位置によって母音を分類するのに使われる。
The vowel triangle is used to classify vowels according to tongue position.
母音四角形 (vowel quadrilateral) is a more detailed four-sided diagram used in some phonetic descriptions, while 母音三角形 is a simpler triangular representation.
Compound of 母音 (boin, 'vowel') and 三角形 (sankakkei, 'triangle'). A straightforward technical term.