As others explained, because a timeshare is deeded, it's real property and therefore should be included. There are two sure-fire ways to exclude them:
1. place a lower limit on your search price as someone suggested (anything below $20k in Virginia Beach is either a time-share or a shack that you couldn't live in even if you wanted to.)
2. find an agent who knows how to search the MLS for you. As agents, we have better search tools, we have access to the REAL database (consumer search sites are mere copies of the database and usually don't include all the data fields in our primary database).
I'm sure you're good at your job and hope you enjoy doing whatever you do. As a professional Realtor, I am very good at my job and I love it. I can grab that database by the ankles and swing it around until your new house comes flinging out. If you don't want timeshares, I'll exclude them from the result set I present to you.