These things are often called name, container and value. Your diagram has them neatly put in columns:

             Name            Container           Value


           +--------+       
Alias:     | $alias | ------------+
           +--------+             |                          
                                  |
                                 \|/
           +--------+       +----------+       +---------+
Variable:  |  $var  | ----> | Variable | ----> | Content |
           +--------+       +----------+       +---------+
                                 /|\                   
                                  +--------+          
           +--------+       +----------+   |          
Reference: |  $ref  | ----> | Variable | --+          
           +--------+       +----------+
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The "variable" label isn't accurate, though, if you also call one of the blocks "variable". And, to more clearly illustrate that an alias is absolutely not a reference, you could consider making the original name and the second name more visually equal:

+--------+ __
| $name  |   \
+--------+    \      +-----------+       +-------+
               ====> | container | ----> | value |
+--------+    /      +-----------+       +-------+
| $alias | __/
+--------+
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And I think the content/value part of Reference is missing in your diagram. It does have one, and that is the actual reference! Hard to draw, though.