Typically, it means that the defendant wants court permission to defend the lawsuit and set aside the judgment that they believe was improperly entered against them. A hearing is set for the court to consider the papers and hear "oral argument." There are lots of circumstances that permit them to get this permission and many circumstances in which they cannot, but you did not specify enough information to know your situation and give a more complete answer.
I assume your questions means that you are the judgment creditor and have obtained a judgment against the judgment debtor. In some circumstances, for example where the judgment was obtained by a default (defendant's failure to answer), the defendant may move to set aside (vacate) the judgment within a certain timeframe. You will have an opportunity to file an opposition pleading and see their reply before the actual hearing on the motion.