HttpContextBase context

Trying to get an explanation in the code bellow: Hope someone can help.

public string GetCartId(HttpContextBase context)
        {
            if (context.Session[CartSessionKey] == null)
            {
                if (!string.IsNullOrWhiteSpace(context.User.Identity.Name))
                {
                    context.Session[CartSessionKey] =
                        context.User.Identity.Name;
                }
                else
                {
                    // Generate a new random GUID using System.Guid class
                    Guid tempCartId = Guid.NewGuid();
                    // Send tempCartId back to client as a cookie
                    context.Session[CartSessionKey] = tempCartId.ToString();
                }
            }
            return context.Session[CartSessionKey].ToString();

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