R17 is a zoning designation that indicates an area is intended for residential use. The R stands for Residential, while the number following it corresponds to the density of housing allowed in that zone. In general, the higher the number after the R, the more dense the housing can be. So, R17 would allow for more houses to be built on a given piece of land than R1 or R2 zoning would.
The specific regulations governing what can be built in an R17 zone vary from place to place and are set by local governments. However, in most cases R17 zones are intended for single-family homes or small multifamily dwellings such as duplexes or triplexes. This means that large apartment buildings would not typically be allowed in an R17 zone.
If you're looking to buy a property with the intention of building a home on it, pay close attention to the zoning designation. If it's zoned for residential use ( indicated by an R followed by a number) then you should be able to build a dwelling there without any trouble. But if it's zoned for commercial or industrial use (indicated by a C or I), then you'll likely need to get special permission from your local government before proceeding with construction.