Expect to come across this important LINQ question in your next interviews. LINQ employs deferred or lazy execution, also known as postponed execution, which means that the execution of a query is postponed until its results are required. Immediate execution, also known as eager execution, refers to the execution of a query as soon as it is defined.   The query is not executed immediately when it is defined with postponed execution, but only when the results are requested. This means that the query is only run when a method like ToList(), ToArray(), ForEach(), or enumerating through it with a foreach loop is called. This enables you to chain together multiple query operations without actually executing any of them until the final result is required.   When you specify instantaneous execution, the query is executed immediately and the results are returned immediately. This means that the query is executed as soon as it is defined, regardless of whether or not the results are required.   One of the primary benefits of deferred execution is that it allows you to make changes to the data source before the query is executed, resulting in more up-to-date results. It also enables more efficient use of system resources; for example, if the query results are not required, the query is not executed, thereby saving resources.