Transhumanism is the idea of using technology to (hopefully) improve the human condition. This can run the gamut from contact lenses to grafting brain implants into fetuses. Think cyborgs.
Books often delve into the question of where the line of human and non-human is, and what is means to be human. Since we don’t really know what it means to be human now (if indeed it means anything), that question gets complicated quickly. Throw in a few rogue AIs and a couple of competing species of runaway nanotechnology, and you’ve got yourself a story.