The Estate Tax is a tax on your right to transfer property at your death. It consists of an accounting of everything you own or have certain interests in at the date of death (Refer to Form 706PDF (PDF)). The fair market value of these items is used, not necessarily what you paid for them or what their values were when you acquired them.
The total of all of these items is your "Gross Estate." The includible property may consist of cash and securities, real estate, insurance, trusts, annuities, business interests and other assets.
Once you have accounted for the Gross Estate, certain deductions (and in special circumstances, reductions to value) are allowed in arriving at your "Taxable Estate." These deductions may include mortgages and other debts, estate administration expenses, property that passes to surviving spouses and qualified charities. The value of some operating business interests or farms may be reduced for estates that qualify.