what actually is orchestration?

> For a small company turning over less than, say, $10m and til now able to work quite comfortably running services on dedicated machines without a dedicated sysadmin/devops team and enjoying the simplicity and stability of Debian, the "orchestration" component seems to be the fly in the ointment of containerisation.

There is no simplicity in Debian on bare metal if you want to deploy complicated applications there. Especially for deployments for more than one machine (e.g a clustered server).

Containers, first and foremost, simplify _deployment_ of applications. And this very much includes small companies.