Expression Trees

• ‘tree like’ data structure
• each node is expression (method call, equality comparison, binary operation etc.) representing a piece of code
• you can compile expression tree and run code it represent
• enables dynamic code generation at runtime
• LINQ queries on DBs are implemented with Expression Trees
• used in the dynamic language runtime (DLR)
• anonymous lambda expression can be converted to ExpressionTree via compiler (i.e. x => x*2 can be represented as tree instead of delegate or anonymous lambda function)

Further read:

https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/expression-trees/