It sounds like you're referring to a save folder or save data location for a game titled "Symphony of the Serpent" — possibly an indie or lesser-known title — and you saw an "upd" (update) guide.
The exact path depends on your operating system. For the most common PC version (Windows standalone or Steam): symphony of the serpent save folder upd
To help you accurately:
global.rmmzsave: Stores global data like unlocked CGs or gallery progress. It sounds like you're referring to a save