It used to be called 'iguchi' (harelip), but now it's called 'koushinretsu' (cleft lip).
Applies to each form listed below
Kanji spelling using 兎 (rabbit) and 唇 (lip); a dated term for cleft lip. The reading いぐち is a gikun/jukujikun.
Kana spelling; may be used to avoid the dated kanji or for clarity.
Alternate kanji spelling using 欠 (lack); also dated and rare.
The kanji 兎唇 literally means 'rabbit lip', reflecting the visual similarity to a rabbit's split upper lip. The reading いぐち is a jukujikun (special kanji reading) not derived from the individual kanji's standard readings.