The discovery? No one really knows what it means (oh joy!). Some think that it was a marker for musicians back in the day, since the term appears at the end of a lot of the Psalms. One guy thinks that the word is really "celah" and means "to weigh." Far fetched, me thinks. Some think that it might relate to a city in the time of David/Solomon known as Selah, and others think that maybe it means forever (think: olam?). There are a few who thought it was merely a marker ending and starting a paragraph. Today it's translated sometimes as "think about it" or "praise the lord." Other times, like in my siddur, it's just selah.
An interesting aside since there's really no answer to this little nugget of prayer that's driving me nuts: Furman Bisher, legendary former sports editor and current columnist for The Atlanta Journal-Constitution, has for decades signed off his columns with "Selah."
Fascinating. Maybe I should make it my life's work to uncover the true meaning of the word selah.