Hishiryo Not-Thinking in Chinese / Japanese...

Hishiryō (非思量) literally means not-thinking.

Hishiryo can be described as a state of mind beyond thinking and non-thinking during the practice of Zazen.

Shiryō (思量) means “thinking,” and hi (非) is a prefix for negation and opposition.

Therefore, hishiryo amounts to “unthink” or “not the matter of thinking.” The word hishiryo appears in Dogen Zenji’s Fukanzazengi, Shobogenzo Zazengi, Shobogenzo Zazenshin, and Keizan Zenji’s Zazen Yojinki. It is one of the most important words used to describe zazen. Hishiryo in these writings comes from a dialogue between Yakusan Igen (745-828) and an unnamed monk, which is described in Keitoku, Dentoroku, and other Zen texts.

The above is an abridged except from School of Shodo: Hishiryo
I suggest you visit that page for a full explanation.