means daily spiritual practice. It is the foundation of all spiritual endeavor. Sadhana is your personal, individual spiritual effort. It is the main tool you use to work on yourself to achieve the purpose of life. It can be done alone or in a group. Sadhana is whatever you do consistently to clear your own consciousness so you can relate to the infinity within you. (https://www.3ho.org/kundalini-yoga/sadhana)
Yogapedia defines Sadhana as the discipline of routine spiritual practice and the routine surrendering of the ego through activities such as meditation, yoga, chanting or prayer.
What it means to me can best be describes as one of my prior Yoga teacher Rex once said, "The way you do anything is the way you do everything."