1942, shortening of stroboscope "instrument for studying motion by periodically interrupted light" (1896), from Gk. strobos "act of whirling" + -scope, from Gk. skopein "to look at, examine."
A spot of higher than normal intensity in the sweep of an indicator on a scanning device, as on a radar screen, used as a reference mark for determining the position or distance of the object scanned or detected.