Forms Data Controls :: Sort Grid View / What Is The Meaning Of Zero

I have this code that once a column in gridview is clicked, it sort the record. Can someon explain to me what does

static Int32 cntsortSecurityID = 0; // declare var to hold 0 or 1 // what is this, I dont understand why. what is the meaning of zero or One in this case . Oh yeas, the code is working for me, but I need to understand the concept behind it.

if (e.CommandName == "sortSecurityID")
{
DataView dv = ((DataSet)(Session["data"])).Tables[0].DefaultView;
if (cntsortSecurityID == 0)
{
dv.Sort = "SecurityID asc";
cntsortSecurityID = 1;
}
else
{
dv.Sort = "SecurityID desc";
cntsortSecurityID = 0;
}
gvTrans.DataSource = dv;
gvTrans.DataBind();
}