One PostgreSQL server for multiple apps?

Hello!

First, I apologize if this email sounds very... novice. I came from MS SQL
Server background, and am recently 'plunged' into a mid-to-long term
project to drop dependencies on proprietary databases, and use PostgreSQL
instead.

Now, in MS SQL Server, I can create a single server to service several apps
together. If the app is a light load and doesn't require something more
than db_owner privileges, I usually just clump them together in the Default
instance, using a new 'database'. If the app has heavier requirements, then
I would spin up a new instance, on the same server (provided RAM and IOPS
requirements suffice, of course).

How would the same principle be applied in PostgreSQL?

Thanks in advance for your kind guide.

Rgds,
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