Librarys

[eluser]seminalJim[/eluser]
What are librarys for, and how do they differ from models and helpers.

I just need to know to keep my code in the right place because as my site becomes more complex im getting confused where to put stuff... eg, im trying to be more modular with my code.

Only difference i know is that helpers are global in controllers and views.

Just to be clear, what are all the differences?

thnks