What is out parameter in sql server? how to use out parameter in stored procedure?

create table emp(eno int,empname varchar(50),sal bigint)

insert into emp values('101','Ravindran','45000')
insert into emp values('102','James','25000')
insert into emp values('103','Mike','15000')
insert into emp values('104','Mathew','5000')
insert into emp values('105','James','18000')

create procedure Emp_return
 @eno int,
 @c1 varchar(50) output
as
Begin
set @c1 = (select empname from emp where eno= + @eno )
return
End

declare @t varchar(50)
exec Emp_return @eno=101,@c1=@t OUTPUT
select @t

using System.Data;
using System.Data.SqlClient;
public partial class _Default : System.Web.UI.Page
{
    SqlConnection sqlcon = new SqlConnection(ConfigurationManager.ConnectionStrings["Con"].ConnectionString);
    SqlCommand sqlcmd = new SqlCommand();
    SqlDataAdapter da = new SqlDataAdapter();
    DataTable dt = new DataTable();
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        string i;
        sqlcon.Open();
        sqlcmd = new SqlCommand("Emp_return", sqlcon);
        sqlcmd.CommandType = CommandType.StoredProcedure;
        sqlcmd.Parameters.Add("@eno", SqlDbType.Int).Value = 101; //pass your textbox value here
        sqlcmd.Parameters.Add("@c1", SqlDbType.VarChar, 50);
        //Get here out parameter like below
        sqlcmd.Parameters["@c1"].Direction = ParameterDirection.Output;
        sqlcmd.ExecuteNonQuery();
        i = sqlcmd.Parameters["@c1"].Value.ToString(); //here i is get out parameter return value
        da = new SqlDataAdapter(sqlcmd);
        Response.Write("Employee Name : " + i);
        sqlcon.Close();
    }
}