Zestimate™ - The Zestimate (pronounced ZEST-ti-met, rhymes with estimate) home valuation is an estimated market value, computed using a proprietary formula. We plunked a Z in front of the word "estimate" to show it is the result of our calculations - and because it's our favorite letter of the alphabet.
Zindex™ - The Zindex home valuation index is the median Zestimate valuation for a given geographic area on a given day. Essentially, it is the middle point. Exactly half the Zestimates for a region are below this number and half the Zestimates are above it. It is expressed in dollars and is for a particular geographic region (e.g., Zindex = $245,000 for Baltimore on July 1, 2005).