How it works
What does on-premises mean, and why does it matter?
On-premises means the software installs on your own computers instead of a company's cloud. There is no server in a distant data center and no copy of the data on someone else's machine, so the reason the data cannot leak is that it never leaves the building.
Cloud software keeps your records on a company's servers and charges you to reach them. On-premises software runs where you are, on hardware you control.
That one difference changes everything downstream: the data stays with you, the system works offline, there is no account that can be shut off, and there is no bill that grows as you add staff.
It installs as an ordinary app, starts on a single office machine, and grows to a shared server later without redoing the work.