The 'scriptural origin' of the term comes from the Book of Abraham, which was
A Translation of some ancient Records that have fallen into our hands from the catacombs of Egypt. The writings of Abraham while he was in Egypt, called the Book of Abraham, written by his own hand, upon papyrus.
In fact, it was completely made up from a funeral document of a very ordinary kind, purchased from a show that passed through his town. Thanks to the Rosetta Stone and true scholarship, a copy of the original scroll has now been properly translated by real Egyptologists. It says nothing of interest to Mormons.
According to a well regarded Mormon source, intelligences are defined as follows:
The word "intelligences" (plural) occurs frequently in LDS literature, having reference to the period of the premortal existence of mankind. The term has received two interpretations by writers within the Church: as the literal spirit children of Heavenly Parents and as individual entities existing prior to their spirit birth. Because latter-day revelation has not clarified the meaning of the term, a more precise interpretation is not possible at present.
Well - how was that for an explanation? In other words even they can't pretend that they know what they are talking about!
They go on to say:
While the revelations leave no doubt [editorial splutter!] as to the existence of intelligent matter prior to its being organised as spirits, speculation sometimes arises regarding the nature of premortal existence.
. . . which makes it all much clearer!
Elder Joseph Fielding Smith gave this caution in 1936:
Some of our writers have endeavoured to explain what an intelligence is, but to do so is futile, for we have never been given any insight into this matter beyond what the Lord has fragmentarily revealed. We know, however, that there is something called intelligence which always existed. It is the real eternal part of man, which was not created or made. This intelligence combined with the spirit constitutes a spiritual identity or individual.
This introduces us to the concept of 'spirit children', who are born into the spiritual realm. They are the children of 'divine beings' (usually deceased Mormons). They grow and develop in the spirit realm until they are ready to be born into the real world - the 'mortal probation'. Their (or should I say 'our'?) memory of the spirit world is 'taken away' so that they can be tested properly in this life.
Whatever 'intelligences' might be, the Mormons believe that they are eternal. They have existed in that form for as long as god has existed, if not longer. This leads on to another surprising fact.
According to Mormons, the universe was not created by god. More on this tomorrow.