Entity Framework (EF) in the context of ADO.NET stands for Entity Framework. It is an ORM (Object-Relational Mapping) framework provided by Microsoft to work with relational databases. EF allows developers to work with data using domain-specific objects, eliminating the need for most of the data-access code that developers usually need to write.

The "DataSource" property is used to bind the DataGrid or DataGridView control to a data source such as a DataTable or DataSet. This allows the control to display data from the specified source. By setting this property, you establish the connection between the control and the data it should display.

The GetChildRows() method of the DataRow object is used to access child rows related to a parent row in a hierarchical dataset. It returns an array of DataRow objects representing the child rows.

A ListBox control allows users to select multiple items at once, while a DropDownList restricts the user to selecting only one item at a time. This makes DropDownList suitable for scenarios where only one option needs to be chosen, such as selecting a category or a state. ListBox, on the other hand, is ideal when users need to select multiple items, such as when choosing multiple items from a list of available options.

In a complex hierarchical dataset, ensuring data integrity involves various strategies, one of which is using DataRelations along with cascading deletes and updates. Cascading deletes and updates automatically propagate changes from parent to child tables, ensuring that data remains consistent across different levels of the hierarchy. This approach simplifies data management and reduces the risk of inconsistencies.

LINQ to Objects queries in-memory collections such as arrays and lists. It's primarily used for querying data structures within the application's memory rather than querying external data sources like databases or web services.

When optimizing LINQ queries for performance, consider using deferred execution. Deferred execution postpones the execution of a LINQ query until the query is iterated over or materialized. This can help minimize the number of database round-trips and optimize memory usage.

When configuring the connection pool for an application requiring multiple concurrent database connections, it's crucial to consider factors such as the maximum number of concurrent users accessing the application and the database server's capacity and limitations. These parameters help determine the optimal settings for the connection pool size to ensure adequate resources for all concurrent connections without overloading the database server.

DataViews and DataTables serve different purposes in ADO.NET. A DataTable represents a single table of in-memory data, while a DataView provides a dynamic view of data from one or more DataTables with sorting, filtering, and searching capabilities.

Connection pooling in ADO.NET involves reducing the number of times connections need to be opened and closed by reusing existing connections, which ultimately improves performance by reducing overhead.