I am confused about the definition of "property". Does it only include real estate? Or also other assets like stocks and bonds?
The Instructions for form 8854 state:
Taxation Under Section 877A. If you are a covered expatriate in the year you expatriate, you are subject to income tax on the net unrealized gain in your property as if the property had been sold for its fair market value (FMV) on the day before your expatriation date (“mark-to-market tax”). This applies to most types of property interests you held on the date of your expatriation.
What do they mean by "property"?