A Repeated Cross-Sectional Data Set A $$Y _ { i t } = \beta _ { 0 } + \beta _ { 1 } X _ { i t } + \beta _ { 2 } W _ { 1 , i t } + \ldots + \beta _ { 1 + r } W _ { r , i t } + u _ { i t }$$

Short Answer

A repeated cross-sectional data set a. is also referred to as panel data.
b. is a collection of cross-sectional data sets, where each cross-sectional data set corresponds to a different time period.
c. samples identical entities at least twice.
d. is typically used for estimating the following regression model
$$Y _ { i t } = \beta _ { 0 } + \beta _ { 1 } X _ { i t } + \beta _ { 2 } W _ { 1 , i t } + \ldots + \beta _ { 1 + r } W _ { r , i t } + u _ { i t }$$