what is using?in c#

using() construct, which is a convenint way to tell C# that when the block of code ends, 
it should dispose the object. If we didn't use it, 
we would instead have to call connection.Dispose(); when we were done. 


Example:

 using(OdbcConnection connection = new OdbcConnection(ConfigurationManager.ConnectionStrings["MySQLConnStr"].ConnectionString))
    {
        connection.Open();
        using(OdbcCommand command = new OdbcCommand("SELECT name FROM test_users", connection))
        using(OdbcDataReader dr = command.ExecuteReader())
        {
            while(dr.Read())
                Response.Write(dr["name"].ToString() + "<br />");
            dr.Close();
        }
        connection.Close();
    }