What is the difference between a metanode and a component?

A metanode is purely organisational. It collapses several nodes into one for readability, and the nodes inside behave exactly as they would on the canvas.

A component has its own scope, can expose a configuration dialog, can carry its own view, and can be shared and reused across workflows or published to KNIME Hub.

So: metanode to tidy up a large canvas, component when you want reusable parameterised logic — a standard cleaning routine applied to every incoming file, for instance.