There are several ways a home could be 'off market', and it depends on which webstie you are looking at. those ways include:
1. It was sold.
2. The listing was cancelled.
3. The listing expired.
4. The home was foreclosed.
5. The home was rented and withdrawn from sale.
6. The owner withdrew it from consideration for other reasons.
Your agent will be able to get you the details.
Doc Stephens, REALTOR