Where is the line between a monitor and a coastal-defence ship?

Where is the line between a coastal-defence ship and a monitor?

A balanced armament suggests a coastal-defence ship; a hull built mainly around a few large guns suggests a monitor, though some designs fit both labels.

The categories overlap: some Norwegian coastal ships later served the Royal Navy as monitors. A practical distinction is that a coastal-defence ship carries a balanced armament for varied local combat, whereas a monitor is organized primarily around one or two very large guns. The Gorgon class demonstrates why the boundary remains porous. The label therefore depends on the whole weapon fit and intended employment, not simply the official class name.