They are defined here: https://github.com/magento/magento2/blob/2335247d4ae2dc1e0728ee73022b0a244ccd7f4c/lib/internal/Magento/Framework/Data/Form/Element/Factory.php#L26-L55
Do you know of any documentation on using these field types?
I am experimenting with some of the different field types on the config page (using system.xml) in a module I am creating to see if there is something that accomplishes what I need.