A taxing district is any entity or unit with the statutory authority to levy a property tax. The areas covered by these districts may overlap and change every year.
In Idaho property taxes are collected by the County and distributed to each taxing district (schools, cities, county agencies, fire districts, road districts, etc.) in which the property lies. The amount of property tax that you pay is based on (1) the assessed value of your property and (2) tax rates and bond debt service amount your taxing districts levy.
For information about Idaho mapping laws for tax districts and other entities, see Idaho Code section 63-215 and IDAPA rule 225.