Difference between user exit/Function exit / Customer exit and BADI

Hi Guys,

I am confused with the types of exits-user exit/Function exit / Customer exit and BADI.

Can you tell me the difference between the different exits/Enhancements?

Classify the following:

what is the one which is shown in SMOD under enhancements? There are 3 sections in that - Function module, Screen and includes.

What is the one which are called using -

Call Customer-Function 001?

Regards,

Guru