No, I'm not familiar with Tulsa. Every city has its own zoning and naming for different types of zones. To further complicate things building codes have similar names for occupancy categories. Realtors that attempt to convey zoning information will sometimes use Building Code occupancy names such as "R3" to say you can build a single family house on a parcel, which is correct for the building code, R3 occupancy includes single family homes, but not necessarily the correct name for the zoning in that jurisdiction.
RS3 at face value might mean something like Residential Zoning, 3 Units. Which may mean 3 units are allowed on each parcel or may mean something like 3 units per acre. I really wouldn't know without diving into Tulsa's municipal code. Density (unit count) is generally displayed on a per square foot or per acre ratio. Such as 1 Dwelling Unit per every 1,000 square feet of lot area. Or 35 Units per Acre. You need to research your lot.