This must be the shekinah glory cloud, indicating the presence of God. It had similarly filled the ancient tabernacle and the Solomonic temple when they had first been dedicated to the Lord (Exodus 40:34; 1 Kings 8:10,11).

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8