what are attributes in c#

An attribute defines additional information (metadata) that is associated with a class, structure, method, and so on. For example you might define an attribute that determines the type of button that a class will display.

Attributes are specified between square brackets, preceding the item to which they apply. Thus, an attribute is not a member of a class. Rather, an attribute specifies supplemental information that is attached to an item.

refer this for more details:

http://msdn.microsoft.com/en-us/library/aa287992%28v=vs.71%29.aspx[^]

hope this helps :)