let's talk about bits baby (#3956)
diff --git a/docs/glossary.rst b/docs/glossary.rst
index 3a1280a..df32760 100644
--- a/docs/glossary.rst
+++ b/docs/glossary.rst
@@ -85,5 +85,14 @@
prefix ``xn--``. To create an A-label from a unicode domain string use
a library like `idna`_.
+ bits
+ A bit is binary value -- a value that has only two possible states.
+ Typically binary values are represented visually as 0 or 1, but
+ remember that their actual value is not a printable character. A byte
+ on modern computers is 8 bits and represents 256 possible values. In
+ cryptographic applications when you see something say it requires a 128
+ bit key, you can calculate the number of bytes by dividing by 8. 128
+ divided by 8 is 16, so a 128 bit key is a 16 byte key.
+
.. _`hardware security module`: https://en.wikipedia.org/wiki/Hardware_security_module
.. _`idna`: https://pypi.org/project/idna/