I have always thought that Aleinu was a piyyut (liturgical poem), not a "prayer" since it does not have a bracha in it.  I was surprised to find that the Wikipedia page for [piyyut](http://en.wikipedia.org/wiki/Piyyut) does not list it, and that the page for [Aleinu](http://en.wikipedia.org/wiki/Aleinu) calls it a prayer.  I realize that Wikipedia may not be the most authoritative source for Jewish answers, so I am asking it here.  Is Aleinu considered a piyyut or a prayer?  Either way, why?  A related (unanswered) question is: http://judaism.stackexchange.com/questions/22674/why-are-ashre-and-alenu-considered-communal-prayers