The first major distinction is between qualitative data and quantitative data. Qualitative data are just data that come in terms of categories like ethnicity and sex and brand name, whereas quantitative data consist of numbers. Qualitative data like this often become quantitative in a sense when we record the number of persons in a group who have that particular characteristic. For this course, the most important type of qualitative data is for situations where there are only two categories. Typically we record the number of persons or things in one of the categories, like the number of males out of n individuals.
Quantitative data comes in a variety of types.
The second type of quantitative data is called ordinal because the ordering of the numbers makes sense, but other uses of the numbers like adding or subtracting them really doesn't make sense. Next Lapin makes a distinction between interval and ratio data. This typology of measurement scales was defined in the 1940's by Harvard psychologist S. S. Stevens. For statistical purposes and for this course, I don't find the distinction between interval and ratio data interesting or useful. So don't worry about telling the difference between the two.