The simplest of the measurement scales is nominal. Within nominal data, each observation is assigned a label, and the only conclusions we can draw are based on whether labels are the same or not, and the frequency with which categories (labels) are chosen.
For example, consider data showing the preferred colors of five people: Blue, Blue, Green, Pink, and Brown. With such data, we can count the number of times each color was chosen, and we can compare people based on whether they gave the same response (e.g., the first two people were the same, but the fifth person was different from the first).
Nominal data is often referred to as being categorical.