Foreign object debris - basically rubbish/litter than can be ingested into engines during high winds, as an example.

Unit loading device. The metal boxes/containers (most common referred to as bins) which luggage and sometimes, cargo, are loaded into. They are then closed up and loaded into the aircraft hold.
Not all aircraft take ULDs, eg 737s. 319s/320s/321s can be configured ULD capable and non ULD capable, the latter known as ‘loose load’.
Terminal 5 is set up for full containerised operations, which is why when a loose load Airbus coming along, like some of the the ex BMI aircraft, they don’t tend to depart on time.
Empty ULDs in high winds pose a risk because they do no have much weight and the wind can catch them.