Handling(tracking) child controls events (only button type child controls) through parent control in data bind controls known as event bubbling.
Server controls like Datagrid, DataList, and Repeater can have other child controls inside them.
Example DataGrid can have combo box inside datagrid. These child control do not raise there events by themselves, rather they pass the event to the container parent (which can be a datagrid,
datalist, repeater), which passed to the page as "ItemCommand" event. As the child control send events to parent it is termed as event bubbling.