diff --git a/product/ERP5/interfaces/business_completable.py b/product/ERP5/interfaces/business_completable.py
index 7ce252a5ec3e492efc4a60825f18eae457bbe9c0..39047c774f99bd9061769350f62721d1b43e5ace 100644
--- a/product/ERP5/interfaces/business_completable.py
+++ b/product/ERP5/interfaces/business_completable.py
@@ -50,6 +50,8 @@ class IBusinessCompletable(Interface):
   def isFrozen(explanation):
     """True if all related simulation movements for this explanation
     are frozen.
+
+    Frozen means that simulation movement cannot be modified.
     """
 
   def getExpectedCompletionDate(task):