noun
crawling on all fours; being on hands and knees
Describes the posture or action of being on hands and knees, often used for babies or when moving low to the ground. Related to 四つん這い (よつんばい).
See also: 四つん這い
赤ちゃんが四つ這いで部屋の中を動き回っている。
The baby is crawling around the room on all fours.
彼は四つ這いになって床に落ちたコンタクトレンズを探した。
He got down on his hands and knees and searched for the contact lens that had fallen on the floor.
Synonymous; 四つん這い is a more colloquial or emphatic variant with an inserted ん.
Compound of 四つ (yotsu, 'four') + 這い (hai, 'crawling', from verb 這う). The reading よつばい is a regular combination.