Préparation is a classical ballet term simply meaning preparation! A preparation step is a position or movement in ballet that prepares a dancer for another, usually more difficult, step.
One of the best examples of préparation is when a dancer does a plié in fourth position before a pirouette en dehors. Another good example would be when a dancer, either a female or male, is posed in a tendu before beginning a menege of turns or coupe jetés.