adv. or adj. phr. 1. With the left or right foot stepping at the same time as another's or to the beat of music; in matching strides with another person or persons. The long line of soldiers marched all in step: Left, right! Left, right! Johnny marched behind the band in step to the music. 2. In agreement; abreast. Often followed by "with". Mary wanted to stay in step with her friends and have a doll too.
Antonym: OUT OF STEP.