Comment by noworriesnate

A modular monolith has a single executable which runs in different modes, typically depending on environment variables. So you can run three processes in the mode that handles web requests, five processes in the mode that processes events on a queue (e.g. Kafka), etc. Eight processes, running in two different modes, but it's all the same executable. That's the basic idea of a modular monolith.

By "plain monolith" I meant just any kind of monolith.