Describes something profound and difficult to grasp, often with a mystical or esoteric nuance. Relatively literary and not an everyday word.
That philosophy book is full of abstruse theories.
His words have a mysterious quality that makes them hard to understand right away.
Composed of 玄 (mysterious, profound) and 妙 (strange, exquisite). The exact historical derivation is uncertain, but the compound has been used in literary and philosophical contexts to denote something deeply mysterious or abstruse.