谁能帮我解释下-----DbParameter对象

String connectionString = "Data Source = .; Initial Catalog = Generate;User ID = sa";
        DbConnection connection = new SqlConnection(connectionString);
        DbCommand cmd = connection.CreateCommand();
         = CommandType.StoredProcedure;
         = "uspGetCustomerById";
        DbParameter parm = cmd.CreateParameter();
        parm.ParameterName = "@id";
        parm.Value = "AROUT";
        cmd.Parameters.Add(parm);


如有以上代码。。。
红色部分如何理解？？
麻烦自豪到的朋友解释下。。
Thank you!