Nominal, ordinal, interval or ratio
Categorical data splits in two. Nominal data is labels with no order, Sales, Design, Finance. Ordinal data has a running order but no fixed distance between steps, Poor, Fair, Good, Excellent. You can say Good beats Fair; you cannot say it beats it by 1.4.
Numerical data also splits in two. Interval data has equal steps but an arbitrary zero, temperature in Celsius, where 0° is not an absence of heat, so 20° is not twice as warm as 10°. Ratio data has equal steps and a true zero, price, weight, hours, so ratios mean something and 20 really is twice 10.
The level decides what you are allowed to calculate. The mode works at every level. The median needs at least ordinal. The mean needs at least interval. Ratios need ratio data.
Label each of the four columns with its level of measurement, Nominal, Ordinal, Interval or Ratio, in row 7.
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