Region / multi-region
The physical geography your compute and database actually sit in, and whether you run copies in more than one of them.
See it
What it is
A region is one specific cluster of datacenters in one geography: 'us-east-1' in Virginia, 'fra1' in Frankfurt, 'syd1' in Sydney. Your functions run in one, your database lives in one, and the distance between them gets paid back on every single query. Multi-region means running copies in several geographies so each user hits the nearest one.
Reach for a second region when your users really are spread across continents and the latency is coming from geography, not from slow code. The cheap version is read replicas in extra regions with one primary that owns all writes. The expensive version is active-active with conflict resolution, and most products never need it.
The classic own-goal: spreading compute everywhere while the database stays in one place. Now every request crosses an ocean, often several times, and the 'global' setup is slower than a boring single-region deploy. Put compute next to data first, then spread out.
Ask AI for it
Inspect the compute and database providers this repo is actually configured for before writing any config. Then pick region identifiers that are valid for those specific providers and that put the app and the primary database in the same region, and declare that region explicitly in the deploy config instead of leaving it on the platform default. Keep every write going to the primary. Add read replicas and read routing only if both providers actually support them; if they do not, say so rather than inventing the feature. Then document the replication lag I should expect and list which routes are safe to serve from a replica and which must read the primary.