Blind baking, the official meaning anyway, is when you pre-cook pastry without the filling. It is used in most sweet pies and tarts, so that the pastry cooks all the way through when you put the filling in.
To blind bake, you put the pastry in the desired pie dish or similar, cover with parchment paper and then weigh it down with any of the following items: raw uncooked rice, baking beans, dried peas or any other pulses. It depends on the size of the pie, but generally you only need to cook it for about 10 - 15 minutes. The purpose of filling the pastry shell with a weighted object is so that the pastry doesn't rise or form air bubbles, which will make it an undesirable vessel to be filled with!
I am happy to say that I am now the proud owner of baking beans! I have only ever used rice before, but it sure is nice to have the fancy version! I did have a bit of a pregnancy-brain moment when I first used them, and didn't line my pastry with parchment. The result, I had to fish out each bean as the pastry had of course started rising and cooking around all the beans! Not my finest moment. But, live and learn!!!