The Estate Tax
The estate tax applies to your heirs' inheritance.
You probably shouldn't worry too much about it, since the estate tax only applies to inheritance in excess of $5.49 million (or twice that, $10.98 million, for married couples—if one partner dies, their cap is added to their partner's). The tax is progressive, capping out at 40% on marginal inheritance in excess of $6.49 million.
The simplest way to reduce the estate tax burden is to give the money away to your heirs before you die. Each heir can receive $14,000 annually as a tax-free gift. Each heir can also receive an additional tax-free lifetime gift of $5.5 million.
This lifetime limit could be spread out over time; for example, each heir could receive $514,000 per year for eleven years, then $14,000 each subsequent year.
Another option involves establishing a trust for your heirs. This is a complex topic; consider speaking with a financial adviser to help you set it up it correctly.