Zone X is outside the 100-year flood plain according to FEMA. Anna gave you a link to the map service where you can put in an address and see what zone a property may be in.
A 100-year flood plain doesn't mean it will flood that area only once in a hundred years, but the rated probability of reaching flood level in any year is 1% inside the zone. A mathematician will tell you that actually that should be called the 50-year flood plain.
The survey will have the current FEMA designation of a property when it's surveyed.
Because most cities have some areas that are not outside a zone (they're zone X), lenders normally require the buyer to obtain flood insurance. It's not that expensive. Usually it does not kill a deal.
Remember that if you don't get flood insurance and your home has rain run in or a retaining wall fall down your homeowners insurance may not cover it. So, just because you're in zone X it still might be wise to pay for flood insurance.