Selah

from wikipedia:
Selah is a word used frequently in the Hebrew Bible, often in the Psalms and is a difficult concept to translate. It should not be confused with the Hebrew word Sela which means "rock".

Selah is probably either a liturgico-musical mark or an instruction on the reading of the text, something like "stop and listen". "Let those with eyes see and with ears hear" is most concise. The Psalms were sung accompanied by musical instruments and there are references to this in many chapters. Thirty-one of the thirty-nine psalms with the caption "To the choir-master" include the word "Selah". Selah notes a break in the song and as such is similar in purpose to Amen in that it stresses the importance of the preceding passage.
Another interpretation claims that Selah comes from the primary Hebrew root word [calah] which means "to hang", and by implication to measure (weigh).
Also "Selah" is the name of a city from the time of David and Solomon.

It is translated into today's general language with the meaning: think about it or praise [the Lord]. Other editions just leave it untranslated as "sela" or "selah"

http://www.mountainretreatorg.net/faq/selah.html :
"But what we do know is that it is a word which means to weigh or measure. And in these contexts, to weigh the preceding words of God and wisely consider them. It is a signature exhortation from God for our thoughtful reflection and weighing of what we have just read."

Psalms 4:4
"Stand in awe, and sin not: commune with your own heart upon your bed, and be still. Selah."

Psalms 9:20
"Put them in fear, O LORD: that the nations may know themselves to be but men. Selah."

Psalms 57:6
"They have prepared a net for my steps; my soul is bowed down: they have digged a pit before me, into the midst whereof they are fallen themselves. Selah."

Psalms 62:8
"Trust in him at all times; ye people, pour out your heart before him: God is a refuge for us. Selah."