Selah - Biblical Hebrew word of uncertain meaning; occurs 71 times in the Psalms and thrice in Habakkuk (3:3, 3:9, 3:13); perhaps a liturgico-musical mark or a reading instruction

"Selah is a word used 74 times in the Hebrew Bible—seventy-one times in the Psalms and three times in the Book of Habakkuk. The meaning of the word is not known, though various interpretations are given below. It is probably either a liturgico-musical mark or an instruction on the reading of the text, something like "stop and listen." Another proposal is that selah can be used to indicate that there is to be a musical interlude at that point in the Psalm. It can also be interpreted as a form of underlining in preparation for the next paragraph. - Wikipedia"