Sometimes a bit of googling works wonders. Have you tried typing "holding the space" in the search box?
If you click on the very first links, you'll get the answer.
..holding space for someone means staying engaged and present with them while they undergo a process of self-inquiry and discovery of truth.
..., when we hold space for someone, we offer ourselves up as a container for the overwhelming feelings they may be encountering due to their circumstances
...When we hold the space for someone we are just present, listening, and validating. We aren't judging, giving advice or offering a solution. We are just there holding their pain, their anguish, their joy, their space.