docs for what bytes means for DNSName, URI, and RFC822Name (#3904)
diff --git a/docs/glossary.rst b/docs/glossary.rst
index a630878..3a1280a 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -79,5 +79,11 @@
but does not allow access to the key itself. Typically an opaque key is
loaded from a `hardware security module`_ (HSM).
+ A-label
+ The ASCII compatible encoded (ACE) representation of an
+ internationalized (unicode) domain name. A-labels begin with the
+ prefix ``xn--``. To create an A-label from a unicode domain string use
+ a library like `idna`_.
.. _`hardware security module`: https://en.wikipedia.org/wiki/Hardware_security_module
+.. _`idna`: https://pypi.org/project/idna/