Resolute Mind in Chinese / Japanese...

決定心 means the mind of certainty, resolute mind, imperturbable mind, firm determination, firm resolution, or stable commitment.

In the context of Buddhism, this is the deep resolution needed to attain enlightenment.

If you go to a deeper meaning, this is a condition of settling into the thought that occurs in the process of perception subsequent to the “seeking mind” or “尋求心.”

This can be translated as unwavering determination, unwavering resolve, or strong determination.

堅定 means unwavering, firm, steady, staunch, and/or resolute.

決心 means determination, resolve, resolution, determined, firm and resolute, or to make up one's mind.

If you want a longer version, 堅定不移的決心 is also a popular phrase with a similar meaning. Contact me if you want that instead.