What does ordinal data mean?

There are four levels of measures, one of them being ordinal. Ordinal data merely orders subjects according to a certain rationale. Numbers indicates a position, indicating that the individual or object possesses more or less of the studied characteristic. As such, an example of ordinal data would be to put all the students in a classroom in order of height, or according to their average in mathematics. However, as we can see, this would not allow to know the height or average of the students. It also doesn't indicate the quantitative difference between each rank. As a consequence, the difference between two ranks does not mean there is a significant difference on what is measured. (Example:1st:95%, 2nd:90%, 3rd: 89%. We would not know the average, only the rank. Also, as we can see, between the first and second rank there is a 5% difference, whereas there is only a 1% difference between the second and third rank.)