In the United States, (and other countries, too), there are several kinds of titles (aka “pink slips"). Unless the title is in order, the motor vehicle department will make your life an expensive, living hell.
CLEAR The name on the bike and the owner's name match. The most desirable situation.
COUNTERSIGNED The title is in someone else's name, but signed off by that person. (Think of a two-party check). The problem is that you have no guarantee the signature is genuine.
ATTACHED The title is held by a second party, typically a finance company or lienholder. You'll need them to sign off on it as well.
JOINT Two names on the title, husband and wife. Both need to sign. Especially important if a divorce is involved, or you may find yourself married (at least financially) to the former owner's ex.
SALVAGE This means the bike was wrecked, and re-purchased from a salvage company. Nothing wrong with this per se, as long as the repairs were done correctly, but it may complicate insuring the new bike, especially for collision (repair damage). A salvage title typically lowers the bike's value substantially.
LOST No title? No deal, unless you intend to break the bike up for parts. Even then you may be on the hook for receiving stolen property. Tell the owner to get the paperwork in order, or you're outta there.