What are these characters from the OS X keyboard?

These are U+fb01 and fb02, Latin Small Ligature Fl and Fi. They are in Unicode really only because they were contained in legacy 8 bit character sets like MacRoman, but should no longer be used for anything. In modern technology such ligatures are created by fonts on the basis of the underlying codes for the separate characters, which is what should aways be input in place of option shift 5/6.

They are called ligatures and they are from the days of metal typesetting. 2 letters that commonly occurred together would be forged as one piece of metal type. Nowadays on the computer, they are sometimes included in fonts, in order to make a more pleasing letter group. They are not special characters, really it is just supposed to be letters f and i drawn together.