diff --git a/Doc/glossary.rst b/Doc/glossary.rst
index 6189cb0..e997d36 100644
--- a/Doc/glossary.rst
+++ b/Doc/glossary.rst
@@ -189,6 +189,10 @@
       A list of bytecode instructions can be found in the documentation for
       :ref:`the dis module <bytecodes>`.
 
+   callback
+      A subroutine function which is passed as an argument to be executed at
+      some point in the future.
+
    class
       A template for creating user-defined objects. Class definitions
       normally contain method definitions which operate on instances of the
diff --git a/Doc/library/asyncio-dev.rst b/Doc/library/asyncio-dev.rst
index ff51c4f..77f8067 100644
--- a/Doc/library/asyncio-dev.rst
+++ b/Doc/library/asyncio-dev.rst
@@ -73,7 +73,7 @@
 executes an ``await`` expression, the running Task gets suspended, and
 the event loop executes the next Task.
 
-To schedule a callback from a different OS thread, the
+To schedule a :term:`callback` from another OS thread, the
 :meth:`loop.call_soon_threadsafe` method should be used. Example::
 
     loop.call_soon_threadsafe(callback, *args)
diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst
index d60a6ce..b1e7318 100644
--- a/Doc/library/asyncio-eventloop.rst
+++ b/Doc/library/asyncio-eventloop.rst
@@ -191,8 +191,8 @@
 
 .. method:: loop.call_soon(callback, *args, context=None)
 
-   Schedule a *callback* to be called with *args* arguments at
-   the next iteration of the event loop.
+   Schedule the *callback* :term:`callback` to be called with
+   *args* arguments at the next iteration of the event loop.
 
    Callbacks are called in the order in which they are registered.
    Each callback will be called exactly once.