It's the what's left after the solids have been boiled away, therefore it doesn't "freeze up" as shea and other butters do when temps drop.
Shea oil is no where as thick as castor oil or even olive and almond. The best I can say is it's like a slightly thicker jojoba and not as thick as sesame. It has all of the pluses and none of the minuses of the parent butter, IMHO.
I figure it mostly absorbs well, but not as well as jojoba. I love this oil as it has a bit more "body" than jojoba w/o the stickiness that comes w/ other heavier oils. I don't use it alone most times, but in combination w/ other stuff, but it's not bad "neat". It has a dryness to it that's similar to the butter it comes from. While I have avocado oil, I'm not familiar enough w/ it to compare the two. It has some of the scent of the original form, but not as intense. I've recently bought some more shea butter to play around w/ to see if I can learn to understand and like it. I tend to dislike all the African butters except coco butter. For my purposes, shea oil (which I always keep and use alot)is the only way (to date) I can stand shea at all.
This is all just my take. I'm glad I came across it because it's very nice. Shea butter, OTOH, kinda sucks.