"Dada" was an art movement in the early 20th century of the European avant-grade.
"Art Nouveau" is a style of decorative art, architecture, and design in western Europe and the US from the 1890's till around World War I, characterized by constant curves.
"Abstract Expressionism" is the movement of American art post World War II. Starting in the 1940's in New York.
"German Expressionism" is and art movement that related to many others in Germany before the first world war.
"Op Art" is a form of art that is created to make an illusion of abstract things moving.
"Pop Art" is art based on modern culture today, especially as a critical or ironic comment on traditional fine art values.