A more thorough explanation:

Definition: Gross up is a slang term used in tax law. It refers to adding back to a deceased person's gross estate the gift taxes paid by the person or their estate on gifts made by the person or their spouse during the three-year period before the person's death. This is defined in the Internal Revenue Code (IRC) section 2035.

Example 1: John gave his daughter a gift of $100,000 two years before he passed away. He paid a gift tax of $20,000 on that gift. When John's estate is being calculated, the $100,000 gift will be added back to his gross estate, and the $20,000 gift tax will also be added back. This is known as grossing up.

Example 2: Mary gave her son a gift of $50,000 four years before she passed away. She did not pay any gift tax on that gift. Since the gift was made more than three years before her death, it does not need to be grossed up when her estate is being calculated.

These examples illustrate how grossing up works in tax law. If a person makes a gift and pays gift tax on it within three years of their death, the value of the gift and the gift tax are added back to their estate when it is being calculated for tax purposes.