Semantically, appending list or plural makes most sense.
However I personally don’t use any plural because I hate having to double check spellings and trying to remember if i made a certain variable/reference plural or singular. Then again I’m not a purist so it’s acceptable to me, to someone who is, they might expect it to be semantically correct.
I probably use “2.) Plural” most often. So long as the names are clearly describing the contents, it’s fine whatever you pick. I’ve never been a big fan of putting the type of the value into the variable name (whether $peopleArray, or hungarian notation).