Orbitals SPDF. Why they named like that?
From the abstract of Structure of the Line Spectra of the Elements as published in the 1890 Journal of the Chemical Society.  


  There are three kinds of series — principal, sharp (well-defined), and diffuse (ill- defined). The principal series form the most vivid lines in the spectra, and only occur in the first, periodic group ; next come the diffuse (really double) lines ...


See also On the Structure of the Line Spectra of the Chemical Elements, also from 1890 by Rydberg:


  Liveing and Dewar were the first to remark the existence of the series, as well as their different appearances. They are of three kinds : diffuse, sharp, and principal series. The first two are formed by the above-mentioned doublets or triplets ...


Later, "fundamental" was added.  

For more information see The Origin of the s, p, d, f Orbital Labels J. Chem. Educ., 2007, 84, 757-758