A Song of degrees
Literally, "of ascents." Perhaps chanted by the people as they went up to Jerusalem to the feasts. See, for example (Psalms 112:1); (Psalms 112:2).
Related Commentaries of Psalms 133:1
Psalms 133:1
1 Behold, how good and how pleasant it is for brethren to dwell togethera in unity!