In Death Note, is it ever revealed what "L" stands for?
In the manga and the anime doesn't reveal what L stands for, but in a especial edition called "Death Note 13: How to Read", reveal that L real name is 


   L Lawliet or in japanese, Eru Rõraito.


Reference: http://deathnote.wikia.com/wiki/Death_Note_13:_How_to_Read