When you die you might have to pay death taxes. The proper name is the Federal Estate Tax. Also most states have an inheritance tax which also must be paid but it is relatively minor compared to the Federal Estate Tax.
If you have assets over $11,200,000 (in 2018), you must pay death taxes. The maximum is 40% on all amounts over $11,200,000 (in 2018). For example if you had an estate of $12,200,000, and you die after 2018, you would have to pay about $400,000 in death taxes if you die.
The law requires that you file an Estate Tax Return, Form 706, within 9 months of the date of death. The death taxes must also be paid at that time. There are substantial penalties if you fail to file the return without a valid excuse and also if you fail to pay the death tax. Usually a lawyer or accountant prepares the Estate Tax Return.