County tax
The part of your property tax that pays for county government. The county's tax need is split among its towns based on each town's equalized value, which is the state's measure of the total market value of the town's property.
New Jersey example
Say your county needs $200 million from property taxes and your town holds 4% of the county's total equalized value. Your town's share of the county tax is $8 million. That amount is then spread across property owners in your town as the county part of the tax rate.
Official source
NJ Division of Taxation - General Property Tax Information (How My Property is Valued)
This is a plain-English summary. Rules and dollar amounts change, so check the official source or a professional before you file or sign anything.