noun
basking; shell drying
Used for turtles and other shelled animals stretching out to dry their shells in the sun. The image is of a turtle spreading its limbs on a rock or log.
池の石の上で亀が甲羅干しをしている。
A turtle is basking on a rock in the pond.
noun
sunbathing on one's stomach
Rare humorous or figurative use for a person lying face down in the sun, likening them to a turtle drying its shell.
He was sunbathing on his stomach at the beach.
Compound of 甲羅 (shell, carapace) and 干し (drying). The word literally means 'shell drying' and originally describes turtles basking in the sun.