This question is not: how do I make a plugin.
This question is not: I need a plugin that does X
This question is literally: how do they work?
I have a project that is coming up that would benefit greatly from modular deveopment - we can create the base system, and then develop the components of the system modularly (as plugins).
I've reviewed the source for Wordpress, and it seems to escape me on how they actually work. Are they a call back?
How would I go about implementing a simplified version of the Wordpress plugin system in custom software?