It means that if you split the profit, then the cost basis of the property should also be split the same way.
For example, if the house was sold for $100,000 which you split with another person 50/50, and the cost basis of the house was $80,000. Then when you report it on your return, you would enter $40,000 as your cost basis and $50,000 as your sale proceeds. That would give you a gain of $10,000 and the other person a gain of $10,000.
**Say "Thanks" by clicking the thumb icon in a post. **Mark the post that answers your question by clicking on "Mark as Best Answer"