Coxswain’s seat (lit. “steering seat”).
Or, the tax district where your company is headquartered, taxable situs (lit. “tax seat”).
The Obama administration is thinking of ways to, unfortunately without the help of the U.S. Congress, prevent U.S. companies from buying a foreign company headquartered in a low-tax country such as Ireland, Holland or Switzerland and then moving their Steuersitz there in order to pay lower taxes. For example, the U.S. government could stop purchasing from companies that do this. That would especially affect enterprises in the health care sector or defense industries (and in the U.S. almost every company provides goods or services to the military).
(SHTOY ah ZITZ.)