When you step and repeat an element using the settings on the S&R tab of the Info palette, you can define the gap between the repeated elements. A gap is the space that exists between elements in a step‑and‑repeat instance. There are two ways of indicating the gap: Gap Size or Displacement Offset. These options are available on the S&R tab only after you define how many times an element is repeated.
Negative gap values can be used, but they will be treated as nested jobs (such as are used in packaging).
Gap size is the distance between two neighboring elements.
Displacement offset is the result of the element's height/width plus the vertical/horizontal distance between each element.