in C# with Example
The in keyword has three uses: a) As part of the syntax in a foreach statement or as part of the syntax in a LINQ query foreach (var member in sequence) { // ... } b) In the context of generic interfaces and generic delegate types signifies contravariance for the type parameter in question: public interface IComparer { // ... } c) In the context of LINQ query refers to the collection that is being queried var query = from x in source select new { x.Name, x.ID, };