Zillow: An internet company that provides online property for sale and rental information. Useful but not always current so check with a real estate professional for up to the minute market information.
Zestimate: An estimate from Zillow on a properties value. However, it is calculated used all house in a radius of the subject property and does not fact in amenities, condition, or even amenities for each subdivision. Even per Zillow, the estimate can be off 25% or more either way