Clicking on an Object to Make it the Variable Target

How could i click a cube and have it because the variable target.

I would like to have this in C# so if that is possible please give it to me like that

I saw this post which is practically what i need but i got errors converting it because it was in javascript

http://answers.unity3d.com/questions/199159/how-to-make-an-object-the-target-when-you-click-on.html

The main problem im getting is the variable ray in that post

This is the script in that post

 var hit: RaycastHit;
 var ray;
 private var target : Transform;
 
 function Update () 
 {
     if(Input.GetMouseButtonDown(0))    // for standalone
        {
          if (Physics.Raycast (ray, hit, 100)) 
            {
               if(hit.collider.gameObject.tag == "TagName")
                 {
                  target = hit.collider.gameObject;
               }
        }
 }

What type of variable is that?