THE WINTER SALES ie "les soldes" will officially begin at 8am, Wednesday 6th January. So brace yourself for exactly 6 weeks of markdowns and price slashes throughout the month and up until Tuesday the 16th February 2016.
Major "soldes" are big thing in France because French laws tightly regulate when stores can and cannot heavily reduce their prices. I'm assuming it was put in place to protect businesses so that the big stores couldn't drive out the smaller ones with their power to discount whenever they wanted, all year round. This way, all stores are treated the same at least regarding the time frame they are allowed to be on sale, regardless of their capacity to slash their prices.