What is nominal/ordinal/interval/ratio scale?

Nominal scale is a measurement in which labels are assigned to variables in order to distinguish them from one-another. The categories in a nominal scale can be arranged in any order and there is no mathematical relationship between them. Ordinal scale is a measure that orders variables in terms of magnitude. In this scale, labels are assigned to variables in categories and the categories are ordered in some meaningful way. Interval scale is a measure in which there is an equal interval between the categories. This interval represents an equal amount of change. In an interval scale, the order of the values is meaningful, but the numerical value of each category has no inherent meaning. Ratio scale is a measure that is similar to interval scale but with the additional meaningful feature that absolute 0 is included as a category. This means that the numerical values associated with each category represent actual differences in the amount of the attribute being measured.