Añejo is a firm, Mexican cheese. It is actually the cheese called "queso fresco" (which is usually made from both cow and goat milk) that has been allowed to age. As it ages, it becomes solid, dry, salty and crumbly, almost like Romano or Parmesan, though it remains more white than they do, looking somewhat like feta cheese. It is used as you would Romano or Parmesan, crumbled, grated or shredded over foods or mixed into them.
Because this starts life as a soft cheese it is often classified as a soft cheese; you may encounter it in varying stages of hardness from semi-firm to hard depending on how long it has been aged.