"上古密约" (Shànggǔ mì yuē) can be translated as "Ancient Secret Agreement" or "Secret Pact of Antiquity". This phrase could refer to various concepts in different contexts, such as:

1. A mythical or legendary agreement made in ancient times

2. A secret pact mentioned in historical or fictional stories

3. A hidden understanding between ancient civilizations

Without more context, it's difficult to provide a specific interpretation or explanation. If you have a particular context or source in mind, please share more details so I can give a more accurate response.

This phrase might also be the title of a book, movie, game, or other media, but I don't have enough information to confirm that. If you're referring to a specific work, please let me know and I'll try to provide more relevant information.