A streamer refers to a direct line of snowfall heading in a straight line, like what's coming off the Cheshire Gap and heading towards Birmingham at the moment.
However, it shouldn't 'really' be used it this circumstance because it really is generally lake-effect snow, which is caused by very cold winds picking up moisture from warm beds of water. You'll often see it in easterly winds on the east coast, with many flurries heading in from the north sea. I'm not entirely sure whether the precipitation shown heading inland at the moment is related to any frontal system or not, so ~
These types of streamers can cause quite significant local snowfalls, as the same area will be experiencing snowfall for a lengthy amount of time, as long as the driving winds last long enough. Doubt it might be the case this time, however.