It is often used in medical terms to indicate a condition or disorder, like:
* Dyslexia: Difficulty reading
* Dysphonia: Difficulty speaking
* Dyspepsia: Difficulty digesting food
* Dysfunctional: Not working properly
* Dystopia: An imagined place or state in which everything is unpleasant or bad
So, whenever you see "dys" as part of a word, it usually indicates a problem or difficulty.