diff --git a/taskflow/engines/action_engine/builder.py b/taskflow/engines/action_engine/builder.py
index cdf36466..9013cd8a 100644
--- a/taskflow/engines/action_engine/builder.py
+++ b/taskflow/engines/action_engine/builder.py
@@ -196,8 +196,8 @@ class MachineBuilder(object):
                 fut = memory.done.pop()
                 atom = fut.atom
                 try:
-                    event, result = fut.result()
-                    retain = do_complete(atom, event, result)
+                    outcome, result = fut.result()
+                    retain = do_complete(atom, outcome, result)
                     if isinstance(result, failure.Failure):
                         if retain:
                             memory.failures.append(result)
@@ -211,10 +211,10 @@ class MachineBuilder(object):
                                 intention = self._storage.get_atom_intention(
                                     atom.name)
                                 LOG.debug("Discarding failure '%s' (in"
-                                          " response to event '%s') under"
+                                          " response to outcome '%s') under"
                                           " completion units request during"
                                           " completion of atom '%s' (intention"
-                                          " is to %s)", result, event,
+                                          " is to %s)", result, outcome,
                                           atom, intention)
                 except Exception:
                     memory.failures.append(failure.Failure())
diff --git a/taskflow/engines/action_engine/completer.py b/taskflow/engines/action_engine/completer.py
index e3ab54d2..1dcb326b 100644
--- a/taskflow/engines/action_engine/completer.py
+++ b/taskflow/engines/action_engine/completer.py
@@ -113,16 +113,16 @@ class Completer(object):
         self._retry_action = runtime.retry_action
         self._undefined_resolver = RevertAll(self._runtime)
 
-    def _complete_task(self, task, event, result):
+    def _complete_task(self, task, outcome, result):
         """Completes the given task, processes task failure."""
-        if event == ex.EXECUTED:
+        if outcome == ex.EXECUTED:
             self._task_action.complete_execution(task, result)
         else:
             self._task_action.complete_reversion(task, result)
 
-    def _complete_retry(self, retry, event, result):
+    def _complete_retry(self, retry, outcome, result):
         """Completes the given retry, processes retry failure."""
-        if event == ex.EXECUTED:
+        if outcome == ex.EXECUTED:
             self._retry_action.complete_execution(retry, result)
         else:
             self._retry_action.complete_reversion(retry, result)
@@ -149,18 +149,18 @@ class Completer(object):
                 unfinished_atoms.add(atom)
         return unfinished_atoms
 
-    def complete(self, node, event, result):
+    def complete(self, node, outcome, result):
         """Performs post-execution completion of a node.
 
         Returns whether the result should be saved into an accumulator of
         failures or whether this should not be done.
         """
         if isinstance(node, task_atom.BaseTask):
-            self._complete_task(node, event, result)
+            self._complete_task(node, outcome, result)
         else:
-            self._complete_retry(node, event, result)
+            self._complete_retry(node, outcome, result)
         if isinstance(result, failure.Failure):
-            if event == ex.EXECUTED:
+            if outcome == ex.EXECUTED:
                 self._process_atom_failure(node, result)
             else:
                 # Reverting failed, always retain the failure...
diff --git a/taskflow/engines/action_engine/executor.py b/taskflow/engines/action_engine/executor.py
index b47322d7..cfc999c2 100644
--- a/taskflow/engines/action_engine/executor.py
+++ b/taskflow/engines/action_engine/executor.py
@@ -35,7 +35,7 @@ from taskflow.types import failure
 from taskflow.types import notifier
 from taskflow.utils import threading_utils
 
-# Execution and reversion events.
+# Execution and reversion outcomes.
 EXECUTED = 'executed'
 REVERTED = 'reverted'