All pickups have coils of wire wrapped around a magnet or magnets. Single-coil pickups have one set of these coils, while dual-coil pickups have two. Dual-coil pickups are typically known as humbuckers because they don’t pick up the hum noise that most single-coil pickups do, they “buck” it.
No engineer’s library would be complete without some technical information, and Ballou’s Handbook, now in its fifth edition, is a serious contender for being your go-to in this field. A university-standard textbook, it’s not for the layperson.