"Searching in parallel" is a technique used to locate avalanche victims with avalanche beacons when there is plenty of manpower available. It can be used by search-and-rescue groups and ski patrols when multiple burials are suspected or the number of buried victims is unknown. The more people that are available, the narrower you can make the search strip for each searcher.
For more information on this technique, visit the research page on the Backcountry Access (BCA) website at http://backcountryaccess.com/research