diff --git a/units/en/unit1/glossary.mdx b/units/en/unit1/glossary.mdx
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@@ -2,6 +2,14 @@
 
 This is a community-created glossary. Contributions are welcomed!
 
+### Agent
+
+An agent learns to **make decisions by trial and error, with rewards and punishments from the surroundings**.
+
+### Environment
+
+An environment is a simulated world **where an agent can learn by interacting with it**.
+
 ### Markov Property
 
 It implies that the action taken by our agent is **conditional solely on the present state and independent of the past states and actions**.