A repeater in ASP.NET is a server control that is used to display a repeated set of data items in a web page. It allows you to create a template for the layout of each item and then bind data to that template, repeating the layout for each item in the data source.

To use a repeater control, you need to first define the layout template for the repeated items using HTML and placeholders for the data. You can then bind the data to the control by setting its DataSource property to a collection of objects or a data source control like a SqlDataSource or ObjectDataSource. Finally, you can call the DataBind method of the repeater control to populate the items with data.

Here's an example of a simple repeater control that displays a list of products: