Definition: A Nominal Scale is a scale in which the numbers serve only as tags or labels to identify or classify the objects. In other words, the nominal scale of measurement deals only with non-numeric variables and there is no relative ordering of the categories, i.e. the numeric value assigned to each category is erratic.
The nominal scale possesses only the description characteristic (unique labels or descriptors used to delegate each value of the scale). Such as the number assigned to the objects under study constitutes the nominal scale. When the scale is used for identification purpose, then there is a strict one-to-one correspondence between the object and numerical value assigned to each object. This means each object has only one number assigned to it, or each number is assigned to only one object. For example, the numbers assigned on a jersey of each hockey player have no value, which tells about the ability of each player, i.e. who is better than whom, rather it is used to identify the players.
When the scale is used for the classification purpose, then the numbers scaled on a nominal basis, serve as tags for the categories or classes. For example, in the case of a gender scale an individual can be categorized either as male or female. The classes or categories are said to be mutually exclusive and collectively exhaustive. This means, the objects in each category are said to be equivalent to the characteristic represented by the nominal number. All the objects in the same category have the same number, and no two classes will have the same number.
It is to be noted that the nominal scale does not determine the amount of characteristic possessed by the object and is only used for counting purposes.