Dada was, officially, not a movement, its artists not artists and its art not art. That sounds easy enough, doesn't it? Of course, there is a bit more to the story of Dadaism than this simplistic explanation.
Dada was a literary and artistic movement born in Europe at a time when the horror of World War I was being played out in what amounted to citizens' front yards. Due to the war, a number of artists, writers and intellectuals - notably of French and German nationality - found themselves congregating in the refuge that Zurich (in neutral Switzerland) offered. Far from merely feeling relief at their respective escapes, this bunch was pretty ticked off that modern European society would allow the war to have happened. They were so angry, in fact, that they undertook the time-honored artistic tradition of protesting.
Banding together in a loosely-knit group, these writers and artists used any public forum they could find to (metaphorically) spit on nationalism, rationalism, materialism and any other -ism which they felt had contributed to a senseless war. In other words, the Dadaists were fed up. If society is going in this direction, they said, we'll have no part of it or its traditions. Including... no, wait!... especially artistic traditions. We, who are non-artists, will create non-art - since art (and everything else in the world) has no meaning, anyway.