Explanation of a product/plugin/template

[flup]

As i today started of with working with the plugin system (yeah, better late then never :P) I was wondering what the difference was between a plugin and a product.

Am I right if I say that:

a product is a collection of plugins/templates bundled together (and thus available for importing them all together in once).
and a plugin is just a loose part of a modification which ads a little part of code to a specific part of vBulletin

If this is correct I do not need to know more