Exempt property is all the property of a debtor which is not attachable (i.e. subject to forced sale) under the Bankruptcy Code or a state statute allowing for sale of property to satisfy debts.
The most common exempt property is the homestead of a debtor, which is nearly always exempt from forced sale.
However, if a lien was obtained for the purchase of that property (such as a mortgage to buy a homestead), the property ceases to be exempt for that purpose.