The word Selah is mentioned in the bible in a total of
seventy-five verses.
There isn't much information nor is there conclusive information
on what is the meaning of the word Selah. Selah a term of
uncertain meaning found in the Hebrew text of the Psalms and
Habakkuk was carried over untranslated into some English versions
The word is first used in 2 Kings Chapter 14 verse 17, where it
was the name of a place which was later renamed Joktheel. This
place which was called Selah was mentioned in relation to
Amaziah the son of Joash king of Judah. Amaziah after becoming
King slew ten thousand of Edom in the valley of salt, and took
Selah by war.
The word is later mentioned within the Psalms at the ending of
certain verses, especially those of David and Asaph. Within the
Psalms it is believed to be a musical note which means to pause,
or reflect. Selah might also represent a instrumental interlude
because the Psalms are supposed to be set to music.
(biblestudyplanet)
In the Book of Habakkuk, Selah is used not only at the end of a
sentence, but also within sentences.