German word Auf
What does this German word actually mean in English?
Words have multiple meanings, so anyone searching for one single, unique "actual meaning" is going to be disappointed.
Especially prepositions are notorious for being used wildly differently in various languages, as soon as you go outside of their core locative meanings and into abstract uses.
It may be best to just learn which preposition goes with which verb or in which set phrase, rather than trying to remember a dozen translations for auf.