I know what it stands for

But we in the UK dont share our national database abroad, so if the phone is from the UK and has been blacklisted through loss or theft, then it goes on the national database and is shared between uk carriers (vodaphone, t-mobile, o2 etc) but the phone is perfectly fine to use abroad as it will not be blacklisted abroad

Its something they are trying to resolve and have the national database shared with the rest of the world as almost all phone thefts in the uk are to sell abroad as there is no comeback

Not sure how it works in the US