I heard ordinal variable is another type of categorical variable. What is ordinal variable?

Glad it helps. ^^

I see, I understand more now.

An ordinal variable is a categorical variable for which the possible values are ordered. Consider a variable like educational experience (with values such as elementary school, high school, some college, and college graduate). Even though we can order these from lowest to highest, the spacing between the values may not be the same across the levels of the variables. Say we assign scores 1, 2, 3, and 4 to these four levels of educational experience, and we compare the difference in education between categories one and two with the difference in educational experience between categories two and three or the difference between categories three and four. The difference between categories one and two (elementary and high school) is probably much bigger than the difference between categories two and three (high school and some college). In this example, we can order the people by their level of educational experience. Still, the size of the difference between categories is inconsistent (because the spacing between categories one and two is bigger than between categories two and three).