An Attribute is a declarative tag which can be used to provide information to the compiler about the behaviour of the C# elements such as classes and assemblies.
C# provides convenient technique that will handle tasks such as performing compile time operations , changing the behaviour of a method at runtime or maybe even handle unmanaged code.
C# Provides many Built-in Attributes
Some Popular ones are
and Many more.
Members please keep on posting more responses providing more In-Built attributes.
Regards Hefin Dsouza