A Run is just a length of a strip observed in a single contiguous observing pass scan, bounded by lines of mu and nu. A strip covers a great circle region from pole to pole; this cannot be observed in one pass. The fraction of a strip observed at one time (limited by observing conditions) is a Run. Runs can (and usually do) overlap at the ends. Like strips, it takes a pair of runs to fill in a length of a stripe. This is why you may read about data taken from "Runs 752/756" or some similar terminology. However, each individual run does contain 6 camcols spanning the same range of nu, but not delimited by eta. These run pairs might not have the same starting and ending nu coordinates.