Blind boxes is a term you'll see cropping up quite a lot on Dinkybox and simply means that you can't tell which figure/keychain/charm etc. you'll be getting. The boxes are sealed and, in many cases, the contents are also wrapped in a foil bag so nobody, not even us, will know what's inside until you open the packaging.
Most of the time, the different figures available will be displayed on the side of the box but, even then, there may be rare, mystery (normally referred to as 'chase'), figures that aren't shown. These are the ones that are very hard to find and are highly prized by collectors.
You might, also, sometimes see numbers, such as 1/20, on the box. These are 'ratios' and tell you how rare that figure is. The number refers to the odds of finding that particular figure. 1/20 = 1 out of every 20 boxes etc. A 1/20 figure is easier to find than a 1/80 for instance.
At Dinkybox, we realise that it can be an expensive proposition to try and complete a collection from just blind boxes so we open a number to give you the chance to finish off a set or find a particularly hard-to-find figure. There's nothing quite like the thrill of opening a box, not knowing what's inside, though so we always do our best to offer blind boxes.