Its' the building value in your case.
On some property tax bills, (such as mine) they call it "improvement value", which is anything that "improves" the land. Could be a building, a fence installed by the land owner, A road, power/communications/water/sewage/drainage lines, etc.
Typically on a tax bill, the total(tax) value is determined by adding together the land value, and any other values used for determining the tax value. In your case, land value plus building value adds up to the total value.
Note that tax values have nothing to do with any other "total" values. In simple terms, the program is asking you for tax values, so that it can determine what percentage of your total cost basis (what you "actually" paid for the property) gets allocated to the land, which is not depreciation, and the percentage allocated to the structure which "does" get depreciated.