A Measuring Cup is a demarcated vessel used to measure liquid ingredients. In the UK, they are delineated in pints and ounces, and in metric. In North America, they are delineated in cups and ounces, and in metric. In the rest of the world, they are delineated in metric.
North America confuses the rest of the world by also using Measuring Cups to measure dry ingredients in addition to liquid ingredients.
One of the difficulties in measuring with cups is that "cups" isn't a term of commerce. Items that are measured in North American kitchens by volume using cups, such as sugar, butter and flour, are actually sold by weight. A pound of flour is always a pound of flour, whether sifted or not, but this is not so for a cup of flour. If you take a cup of flour and sift it and put it back in the cup, you will now have more than a cup of flour because the added air in the flour will have increased the volume of it. Another example is a cup of walnuts: whole, halved, chopped, and ground will all yield a different weight of walnuts.
In an attempt to control this possible disparity, recipe writers will often attempt to describe precisely how they want you to put the ingredient in the cup by using adjectives such as generous, loosely-packed, tightly-packed, scant, rounded, heaping, sifted, level, etc.
Coffee machine makers seem now to refer to a cup as something that must be a 100 or 125 ml (3 or 4 oz) cup. Their cup measurement doesn't match up with any kitchen Measuring Cup, let alone any coffee cups or mugs that anybody actually uses to drink out of. But they can do that, as cup is not a legally defined term.