What does @@ and @a suffixed by property names specify in sql server 2008?

In this post we will discuss about @@ and @ used in sql server 2008. Also you can check out my previous posts on:

- Single stored procedure to insert update and delete in sql server 2008

- Serialization and Deserialization in Remoting in C#.Net

- Activation Models in Remoting in C#.Net

@@ and @ are frequently used in sql server.

@@ -> This is used for the Global variable declaration.

Ex:
@@Error=0

@- >This is used for the variable declaration

Ex:
@address  varchar(30)