[0ct4via]

In-cabin FOD can be things like loose pens (or even just pen lids/caps), iPads/books, etc. - which is why there are generally rules (admittedly more in the military, because they like that sort of thing) about ensuring things either meet certain FOD requirements/regulations (i.e. pens with screw-on caps, fitted in specific pen pockets, rather than one with a cap that could slide off, loose in a regular pocket), so ensure they don't end up interfering or blocking controls, etc.

As for outside the aircraft, FOD can cover anything from loose rubber / screws, etc. on the runway that could end up damaging the tires or being taken through the engines, to in-flight FOD risks like bird strikes and volcanic ash - which obviously are also foreign objects that risk damage to the aircraft.