How Input and Output Work

Inputconvert from a textual form to an expression
Processingdo computations on the expression
Outputconvert the resulting expression to textual form

Steps in the operation of the Wolfram Language.

When you type something like x^2 what the Wolfram Language at first sees is just the string of characters x, ^, 2. But with the usual way that the Wolfram Language is set up, it immediately knows to convert this string of characters into the expression Power[x,2].

Then, after whatever processing is possible has been done, the Wolfram Language takes the expression Power[x,2] and converts it into some kind of textual representation for output.

The Wolfram Language reads the string of characters x, ^, 2 and converts it to the expression Power[x,2]:
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This shows the expression in Fortran form:
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FortranForm is just a "wrapper": the value of Out[2] is still the expression Power[x,2]:
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It is important to understand that in a typical Wolfram Language session In[n] and Out[n] record only the underlying expressions that are processed, not the textual representations that happen to be used for their input or output.

If you explicitly request a particular kind of output, say by using TraditionalForm[expr], then what you get will be labeled with Out[n]//TraditionalForm. This indicates that what you are seeing is expr//TraditionalForm, even though the value of Out[n] itself is just expr.

The Wolfram Language also allows you to specify globally that you want output to be displayed in a particular form. And if you do this, then the form will no longer be indicated explicitly in the label for each line. But it is still the case that In[n] and Out[n] will record only underlying expressions, not the textual representations used for their input and output.

This sets t to be an expression with FortranForm explicitly wrapped around it:
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The result on the previous line is just the expression:
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But t contains the FortranForm wrapper, and so is displayed in FortranForm:
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Wherever t appears, it is formatted in FortranForm:
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