The article is devoted to the peculiarities of the special musical terminology in the German epistolary text of the 18th century, in particular, in the letters of Wolfgang Amadeus Mozart. Using the example of the use of polyphonic terms, namely the term “fugue”, the context of mentioning this musical form and its interpretation in the letters of Mozart is analyzed. The composer’s epistolary material indicates that Wolfgang Amadeus’s interest in fugue did not arise in early life in Vienna (familiarity with the fugues of JS Bach and GF Handel at the meetings of Baron van Swieten), but much earlier. The term “fugue” and the associated vocabulary are interpreted in these epistolary texts unambiguously and do not cause discrepancies in the translation.