Sizing in labels is a little different to regular artwork sizing. Rather than things being measured with the terms Width, and Height, we use the terms Short Edge, and Long Edge.
Short Edge is the shortest length of measurement on a label. For example, if your label was 30mm wide, and 55mm high, the Short Edge would be 30mm (the width). Long edge is the opposible and describes the longest sides of the label. With the above measurement, we would title the 55mm Height as the Long Edge.
Understanding Short and Long edge is important, because if you're not certain what roll direction you need, understanding whether it needs to be short edge first, or long edge first, could make things a lot easier for you.
This might not matter as much if you're applying these labels by hand, but it could also make things significantly easier, even if you don't have an applicator with strenuous requirements. For example if you look at the image below and you have labels for your new Craft Beer, it will be easier to apply them from the Left Edge or the Right Edge (in this case these would be the short edge), rather than from the Top. This will allow the label to roll around the can and will make the application process smoother than if you're placing it from the top. In this case below, a label with either Short Edge leading, would be ideal.
