Added information about Online project hibernation

architecture/core_concepts/projects_and_users.adoc

@@ -146,6 +146,26 @@ include any application objects for access by multiple projects, such as
 templates and images. These objects should be those that do not require
 communication between the pods.
 
-
-
-
+ifdef::openshift-online[]
+[[projects-hibenation]]
+=== Project Hibernation
+In {product-title} Starter, a project exceeding 16 cumulative quota-hours of
+usage in a rolling 24-hour period must sleep, or _hibernate_, for the next 18 hours.
+
+In {product-title} Pro, projects do not hibernate.
+
+Quota-hours are calculated as the maximum between percentage of terminating and
+non-terminating pod resource quota consumed, multiplied by the running time of
+those pods. For example, 2 terminating pods each using half of the available
+memory quota for 1 hour will be counted as 1 terminating quota-hour.
+
+When the project is in hibernation, the replica count is set to `0` and all
+individual pods are deleted. All PVCs and PVs in the project are left untouched.
+After the hibernation period is over, a project is put in an idled state, where
+the replica count is `0`, but the force-sleep resource quota is removed. Upon
+receiving network traffic, the project's replica counts will be restored to
+their pre-hibernation value and pods will be created.
+
+If network traffic does not restore a project's replica counts, then you may
+have to manually scale up the deployment.
+endif::[]