diff --git a/ansible/readme.md b/ansible/readme.md
index eb5ae1c..462a44d 100644
--- a/ansible/readme.md
+++ b/ansible/readme.md
@@ -3,6 +3,33 @@
 Lives here, beside the app it deploys, the way the other apps on this machine do.
 It owns the `menu-app` container and the Site's snippet in the shared Caddyfile.
 
+## Words used below
+
+The deployment reads as jargon if you have not done one before, so:
+
+- **web address** — one hostname the web server answers for. Caddy keeps a block
+  per address; `menu.hopsngrains.com` is one. Older writing calls this a
+  _vhost_, which just means "virtual host", and `vhost` is the variable name in
+  `vars/`.
+- **parallel run** — putting the app on a second, temporary address
+  (`menu-new.hopsngrains.com`) while the old site keeps the real one, so the new
+  one can be checked on a phone without customers seeing it. It needs a DNS
+  record for the temporary name, because Caddy has to fetch a certificate for it.
+- **cutover** — the moment the real address is pointed at the new app instead of
+  the old nginx container, and that container is stopped. Customers are on the
+  new app from then on. It is reversible.
+
+| Stage         | Address customers use              | Address you check                     |
+| ------------- | ---------------------------------- | ------------------------------------- |
+| today         | `menu.hopsngrains.com` → old nginx | —                                     |
+| parallel run  | unchanged                          | `menu-new.hopsngrains.com` → this app |
+| after cutover | `menu.hopsngrains.com` → this app  | —                                     |
+
+Skipping the parallel run is a legitimate choice: cutover on its own is one
+command, one Caddy reload, and a rollback if anything looks wrong. The parallel
+run is for finding out that a container will not start, or a font will not load,
+without anyone watching.
+
 ## What lives where
 
 | Thing                                  | Where                                                                       |