diff --git a/docs/what_tests_can_be_run.md b/docs/what_tests_can_be_run.md
index b7dc50d3482d57e507fa890c22af1db1ed90aa55..1970973db77a98a86a626503562c4bd42d5b7a0c 100644
--- a/docs/what_tests_can_be_run.md
+++ b/docs/what_tests_can_be_run.md
@@ -18,7 +18,12 @@ Orchestrated tests are run with the `gitlab-qa` binary (from the
 (useful if you're working on the `gitlab-qa` project itself and want to test
 your changes).
 
-These tests spin up Docker containers specifically to run tests against them.
+These tests spin up Docker containers specifically to run tests against them.  These containers are created from the Dockerfile in the omnibus-gitlab project. As shown in the examples below, these containers can be based on
+
+* the `nightly`-tagged Docker image, which is built daily and reflects the master branch at the time of the build
+* the `latest`-tagged image, which is built from the latest released stable version
+* a custom image (e.g. one built from a earlier released version)
+
 Orchestrated tests are usually used for features that involve external services
 or complex setup (e.g. LDAP, Geo etc.), or for generic Omnibus checks (ensure
 our Omnibus package works, can be updated / upgraded to EE etc.).