An attitude in classical ballet is a position where the dancer is standing on one leg with the other lifted, usually to the front (devant) or back (derrière). The leg in the air is bent at the knee so that it forms roughly a 145 degree angle.
The attitude position is commonly seen throughout many aspects of classical ballet technique in class and on stage in classical and contemporary choreography.
It is important for a dancer not to over, or under, bend the leg in attitude causing the lifted and bent leg to look either too short or too long (possibly being mistaken for an improper extension with a bent leg, for example an arabesque with a bent leg working leg is not an arabesque.)