A bizarre morning ritual in which many women apply massive amounts of makeup and try to dress in the latest "smart but sexy" fashion, load their two tiny children into the back of a vast people carrier or Chelsea Tractor and drive them the 1.5 miles to school.
Once outside the school they double-park, unload the squalling sprogs and walk them to the school gates where they can ostentatiously bid their appalling offspring an apparently fond farewell while at the same time comparing and contrasting themselves and their makeup and attire against those of all the other women doing exactly the same. A few false compliments and veiled verbal knifings are delivered this point and in some cases, the women will split into small gaggles in order to better gossip and belittle the non-members of their particular pack.
The school run is a relatively new phenomenon and has risen in importance along with the growth of ostentatious prosperity (see also chav, WAGs, Posh Spice). Initially provoked by fearmongering scare stories in the right-wing press about how paedophiles lurk on every street corner and sweetshop, it soon become unacceptable to entrust one's precious darlings to the School Bus (now only used by those children whose parents have a deficiency of time, money or inclination to backstab each other) or, God forbid, let the little sods walk to school.