A miniature is when something that is usually big is done smaller. Miniatures can go from an artform on a smaller scale, like painting or origami, to everyday objects recreated smaller. The everyday objects that are made smaller can be of interest for collections of that specific object, for example, a fan of airplanes can have small models of planes. They can also be really appealing as accessories for other types of collection, for example, for action figures, chairs, houses, cars and food can be bought to fit with the figure.
Of course, since there are so many different sizes, miniatures are measured in scales. The scale of a miniature determines how small it is compared to the original object. An example of a scale is 1/12, this means whatever the miniature is, it is 12 times smaller than the original. So if you want to buy accessories for another miniature, the best is for all the accessories to be on the same scale.