overview

The standard query operators are extension methods of IEnumerable<T> or IQueryable<T>. They are the static methods of the Enumerable and Queryable classes.

manner of execution

Standard Query Operator methods can execute in immediate or deferred manner.
If deferred, in streaming or non-streaming forms.

deferred queries

A deferred query fetches the updated data from the data source each time query results are iterated. A deferred query can be forced to execute immediately with Enumerable.ToList or Enumerable.ToArray.

query operators with equivalent query expression clauses