Let me attempt to make a long story short.
In koine Greek (the Greek of the New Testament and of the Septuagint--the Greek translation of the Hebrew Bible) the standard word for "glory" is kleos. It is used for the fame, renown, or reputation someone can gain as a result of their notoriety. The Septuagint translators chose not to use this word to translate the Hebrew kabad, most often translated "glory," but almost always only in reference to God.
They chose instead the word doxa, which, as a noun in ancient Greek, usually means an "opinion," "belief," and sometimes, "reputation" (it still hads this sense in our English word "orthodoxy"). One can guess (no one knows for sure) that doxa was chosen to have a fresh word not tied up in definitions about the "glory" of human beings. Nevertheless, in choosing the word doxa, they fundamentally changed its meaning, not only from "opinion" to "glory," but from something totally subjective to one, in its use to describe God's nature and being, totally objective.
"Glory," whatever Hebrew or Greek word it is translating, is difficult to define. I think it is best to be thought of as a word that describes, as I just said, the very nature and being of God. It can have the connotation of "light," "wonder," "mystery," "awe," "perfection," just about any word you could find to describe God.
The New Testament, by the way, follows the use of the Septuagint. The original word for "glory," kleos, appears only one time, in 1 Peter 2:20. It was translated as "glory" in the King James Version, but not since then. Doxa appears at least 150 times.
The New Testament takes the word further, however, and ascribes it to humankind, but only in the sense of our being able to participate in the divine glory, or, as Paul says in 2 Cor 3:18 (where the title of this blog comes, through its use by Charles Wesley),
And all of us, with unveiled faces, seeing the glory of the Lord as though reflected in a mirror, are being transformed into the same image from one degree of glory to another; for this comes from the Lord, the Spirit.
This use of glory, in reference to us is eschatological in nature, that is, it pertains to our hope, as Paul says in Colossians 1:27:
To them God chose to make known how great among the Gentiles are the riches of the glory of this mystery, which is Christ in you, the hope of glory.
In a sense, this use in the New Testament, of "glory" being something in the divine nature that we can ultimately share, brings the use of the word back around both to the kleos and the original doxa meaning, except that the glory in which we come to share neither originates from ourselves nor is subjective. It is in the realm of "faith, hope, and love," Paul's big three (1 Cor. 13:13).
That's what I have so far. It's a great deal on which to chew.