Rashi is discussing whether the word עזרא is spelled with an aleph (in which case it would be the Biblical person) or with a heh (in which case it would be the Temple's main courtyard).
Rashi writes:
ספר תורה של עזרא ואני שמעתי עזרה בה' ופי' ספר מוגה היה בעזרה שממנו היו מגיהים כל ספרי גולה
That is, first with an aleph, in which case it was the Biblical Ezra's copy of the Torah. Ezra was instrumental in reestablishing the Torah's study and practice. Rashi continues: And I heard Azara with a heh (rather than final aleph), and its meaning would be a corrected Biblical text, which was in the courtyard, from which they would correct all the Biblical books of the Diaspora.
Compare Masechet Soferim, which talks about three variant sifrei Torah found in the Azara, and how they used a democratic process to reestablish the correct Biblical text my following the majority reading.