The Execute Package Task is a task in SSIS, executing an already deployed package (a child package) from a parent package.
Basically, it contains a reference to the child package, but since it's used from the parent package, the developer can set transaction options for the packages in the ETL process flow.

For more information about changes to this task in the SQL Server 2012 release of SSIS, see the Execute Package Task topic in Books Online.

For the complete list of SSIS tasks, visit this page.