The Collaborative International Dictionary of English v.0.48:

Maypole \May"pole`\, n.
   A tall pole erected in an open place and wreathed with
   flowers, about which the rustic May-day sports were had.
   [1913 Webster]

WordNet (r) 3.0 (2006):

maypole
    n 1: a vertical pole or post decorated with streamers that can
         be held by dancers celebrating May Day