In Death Note, is it ever revealed what "L" stands for? In Season 2, we meet L's successors, "M" (Mellow) and "N" (Near). Seeing how they are his successors and were all raised in the same institute, L must also stand for something.
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