But it stands for General Instruction on the Liturgy of the Hours. Promulgated in 1971, it is the official guide from the Church's magisterium regarding all thing Divine Office. It's about 70 pages of fine print, and covers every topic you can imagine.
The GILH devotes chapters to the Importance of the Liturgy of the Hours, the Santification of the Day and description of each liturgical hour, the individual elements of the hours, the Various Celebrations in the Church Year, and Rites for Celebrating the Hours in Groups.
You can find this document here on the EWTN library website. It also appears in its entirety in the first volume of the four-volume breviary. The one-volume Christian prayer only contains excerpts. Most people, even those who like the Divine Office, won't be inclined to read it all in one sitting. But it's the best reference there is. For motivation to stick to your daily recitation of whichever hours you use, the first two chapters can't be beat.
I'm going to start a series on the GIHL which should last a good long time, since its five chapters contains 284 sub-sections. What I'll do is reprint a short passage from the GIHL, and then maybe, if it seems necessary, add some comments of my own. As always, I'll invite comments on my comments, because my only qualification for commenting at all on Church teaching is that I'm a Catholic who can read. (Well, there were 12 credits towards a Masters in religious studies 27 years ago, but they've since expired) This will happen on days that I feel like posting but am not all wide-eyed and breathless over some particular psalm or reading from the day's office, or its saint.
I know that lots of people are allergic to reading Church documents. They have good intentions, and often resolve to try an enclyclical or an exhortation, but soon find themselves getting itchy from all the dryness, or succumb to sleep apnea brought on by too much inscrutable philosophy and theology. Or, like me, they're just lazy and would rather read a novel. But I hope you'll check it out whenever there's a "GILH" in the post title. I promise we'll take it in very small bites.
So stay tuned.