What is a Writ of Execution for a debt that I dont know about?

A Writ of Execution means that someone has obtained a judgment against you. The Writ of Execution is issued by the Court to allow the constable to seek to collect the judgment. Of course, most people don't have any assets to satisfy such judgments and the Constable will normally file papers with the Court stating that he investigated and found no assets. The Writ may mention what judgment is involved. With that information, you or an attorney could track down the original lawsuit and determine what, if any, options you may have at this point.