UCLA WhatStat offers very good definitions of variable types used in statistical analysis. I expand on that and summarize as below:
Categorical variable(called nominal variable): has two or more categories, but there is no intrinsic ordering to the categories.
Ordinal variable: is similar to a categorical variable. The difference between the two is that there is a clear ordering of the variables.
Interval variable: is similar to an ordinal variable, except that the intervals between the values of the interval variable are equally spaced.
Dummy variable(indicator variable): A categorical variable that has been dummy coded. Dummy coding (also called indicator coding) is usually used in regression models, but not ANOVA. A dummy variable can have only two values: 0 and 1. When a categorical variable has more than two values, it is recoded into multiple dummy variables.
Nominal variable:
