C# picture box why use this +x+ : why use +x+ in imagelocation

     private void CreateEnemies()
        {
            Random rnd = new Random();
            int x = rnd.Next(1, kindOfEnemies + 1);
            PictureBox enamy = new PictureBox();
            int loc = rnd.Next(0, panel1.Height - enamy.Height);
            enamy.SizeMode = PictureBoxSizeMode.StretchImage;
            enamy.ImageLocation = "Aliens/"+x+".png";

        }

I don't understand why use this +x+ for search image location.