Ruach (Roo-akh) Ha-Kodesh, a Hebrew term literally meaning Spirit of Holiness, is a level of inspiration that is just below that of Nevuah. According to the Rambam in the Moreh Nevuchim (Guide for the Perplexed,) this is simply an abnormally intense intellectual understanding, such that it is clear that it is from beyond you, but is still a purely intellectual understanding that can be understood by others. This is not he level of Nevuah, or true prophecy. All the books of the bible were written with Nevuah, but the Mishna and Talmud were written with Ruach HaKodesh.

This term is also sometimes used, in a (gramatically) very odd sense, by christian missionaries, to refer to the holy ghost. and more grammatically correct way to do this would be Haruach Hakodesh.