When you are producing a map at a scale in which the labels are large with respect to the features, or there are numerous features in a small area, you may need to decide whether to not label features where conflicts occur or modify the labels so that more will fit. The Maplex Label Engine includes a number of space-saving strategies.
Labels can be stacked, extended beyond features, reduced in size, abbreviated or truncated, or labeled with a key. You can apply one or more of these strategies to produce the best result for your map.