The default title for the bibliography in an article
-like class is "References", in a report
/book
-like class it is "Bibliography". These names are stored in \refname
and \bibname
, respectively.
It is a bit tricky to overwrite \refname
and \bibname
directly, since both biblatex
and polyglossia
/babel
redefine these strings when the language is changed. That means that a change you make may be made undone at begin document (when the document language is set up) or whenever languages are switched.
With a current version of biblatex
the prettiest solution probably uses \DeclarePrintbibliographyDefaults
\documentclass{report}
\usepackage{polyglossia}
\setmainlanguage{english}
\usepackage{csquotes}
\usepackage[backend=biber, style=authoryear]{biblatex}
\DeclarePrintbibliographyDefaults{title=\refname}
\addbibresource{biblatex-examples.bib}
\begin{document}
Lorem \autocite{sigfridsson}
\printbibliography
\end{document}

But for a one-off you could just use
\printbibliography[title=\refname]
instead of \printbibliography
In biblatex
contexts, biblatex
controls \bibname
and uses its bibstring bibliography
for that, so
\DefineBibliographyStrings{english}{
bibliography = {References},
}
would also work.
babel
if you want, because it supports these three languages.\printbibliography[title=References]
should work.