The Holy of Holies had a veil (which was very thick, more akin to a wall) separating it from the people. When Jesus died, this veil was torn in two — from top to bottom. This is significant for two reasons.
First, being torn from the top down, signifies it was God’s doing. Since it was thirty feet high, a person would only be able to tear it from the bottom up. In effect, God was saying, I’m changing the old way of doing things.
More importantly, this opened up the Holy of Holies, showing that everyone could now approach God, at any time — not just the high priest once a year.
Some translations refer to the Holy of Holies as “the Most Holy Place” or “the Holiest of all.”