Consumerism can be translated as the act of consuming products or services without the need.
Since the industrial revolution of the XVII century, the products are produced so quickly (fast) and in much quantity. The society through, for example, advertising is attracted by advertisements of all media (newspapers, television, cinema, ...) and eventually consume products that are sometimes unnecessary, without interest and need.
The definition of need superfluous, can be subjective, not everything is redundant or are no products that meet the need of people, but most times not all people.
I leave here a rhetorical question: "Who has not consumed anything that after you saw taht it was unnecessary?"
Everybody as well as me (I think), we are consumerists (but I am not compulsive and extremist). We are immersed in a society that interacts with and propagates the "fever" of alienated consumerism. This is the effect of Capitalism.
Here's some more ideas and definitions, purpose of this theme through these websites dedicated to these two philosophers: Gilles Lipovetsky
( http://www.phease.org.nz/~leon/oldsite/history/commodities.htm )
and Jean Baudrillard
( http://marginalutility.blogspot.com/2005/05/notes-on-jean-baudrillard-consumer.html ).