The list of people you have to or want to say "hello" to on a daily basis. Especially relevant for students in university buildings, or coworkers in a workplace. Some people might decide to put you on their hello lists, even if they aren't on yours! Typically, reciprocity is expected.
Dropping someone from your hello list to just a nod when you pass him or her might be considered a snub by the other person.
Prices shown in USD.