Slam poetry is a form of performance poetry that occurs within a competitive poetry event, called a "slam", at which poets perform their own poems (or, in rare cases, those of others) in as nuanced a performance as the performer can muster and as the material can bear - with an eye to the audience who vote on such things.
Critics of Slam poetry say that the quality of the performer often wins the day irrespective of the quality of the poetry. Its defenders say that this is like saying a poem printed in the finest type on the most exquisite paper will win the Pulitzer Prize for poetry.
In the view of its exponents, the point of Slam is to challenge the authority of anyone who pretends to know absolutely what quality is. Additionally, it seems that the poets that embrace Slam poetry wish to give audience members the power to become part of each poem's presence, thus breaking down the barriers between poet/performer, critic and audience.
Slam poetry has always had some degree of connection to rap music, with both styles of expression involving rhythmically delivered phrases. Notable slam poet (as well as actor, activist, rapper and author) Saul Williams has contributed to the blurring of the lines between the two art forms, and many underground hip hop MCs have drawn influence from slam poetry (including Mos Def, Sage Francis, both of whom started performing at poetry slams before successful careers as rappers)