וְה֤וּא יָצָא֙ וַעֲבָדָ֣יו בָּ֔אוּ וַיִּרְא֕וּ וְהִנֵּ֛ה דַּלְת֥וֹת הָעֲלִיָּ֖ה נְעֻל֑וֹת וַיֹּ֣אמְר֔וּ אַ֣ךְ מֵסִ֥יךְ ה֛וּא אֶת־רַגְלָ֖יו בַּחֲדַ֥ר הַמְּקֵרָֽה׃
Now when he was gone out, his servants came; and they saw, and, behold, the doors of the upper chamber were locked; and they, said: ‘Surely he is covering his feet in the cabinet of the cool chamber.’
Metzudat Zion on Judges
It is a euphemism for reliving himself as an Samuel 1:24:3 "And Saul came to relive himself." Its named this based on the way that he is sitting down and facing. To shut in and to cover his legs because of modesty.