thick hide; shamelessness
Literally refers to thick animal skin; figuratively describes a person who is thick-skinned, brazen, or shameless. Often used in the phrase 厚皮をかぶる or similar expressions.
He's thick-skinned, so he doesn't mind a little criticism.
That politician shamelessly told the same lie again.
Compound of 厚 (あつ, 'thick') and 皮 (かわ, 'skin'). The figurative sense of shamelessness derives from the idea of having a thick skin that is impervious to criticism.