Spiritual Karma Yogas, what is spirit?

Under the spiritual Yogas section in Kala one Yoga reads:

"The 9th lord a strong benefic with or aspected by Jupiter or Venus indicates that the native will engage in the recitation of prayers, holy contemplation, or abstract meditation on the nature of Spirit, according as the navamsa occupied by the 9th lord belongs to a movable, fixed or dual rasi."

I am wondering what is the Sanskrit word that is being translated as Spirit in this case and what is the source?  Thank You!