What's a barrage in cycling?

Recently there was a small maelstrom caused when the commissaire of La Vuelta Femenina decided to "barrage" Niamh Fisher-Black during stage five, but allowed Mavi Garcia another rider through.

Some may be wondering what a barrage is. Essentially it's a technique used by race officials to impede the progress of team cars (the "caravan") at times when they would affect the outcome of the race, specifically when they would allow dropped riders to regain a group they were dropped from.

So instead of letting the cars drag Niamh back to the front of the race via drafting the commissaire intentionally stops the cars and forces Niamh to ride back to the group herself without the aid of a moto-pace.