The Collaborative International Dictionary of English v.0.48:

Blotting paper \Blot"ting pa`per\ (p[=a]`p[~e]r).
   A kind of thick, bibulous, unsized paper, used to absorb
   superfluous ink from a freshly written manuscript, and thus
   prevent blots.
   [1913 Webster]

WordNet (r) 3.0 (2006):

blotting paper
    n 1: absorbent paper used to dry ink [syn: blotting paper,
         blotter]