feature: add drain to glossary

Author: abhilasha2418

content/en/docs/reference/glossary/drain.md

@@ -0,0 +1,18 @@
+---
+title: Drain
+id: drain
+date: 2024-12-27
+full_link:
+short_description: >
+  Safely evicts Pods from a Node to prepare for maintenance or removal.
+tags:
+- fundamental
+- operation
+---
+The process of safely evicting {{< glossary_tooltip text="Pods" term_id="pod" >}} from a {{< glossary_tooltip text="Node" term_id="node" >}} to prepare it for maintenance or removal from a {{< glossary_tooltip text="cluster" term_id="cluster" >}}.
+
+<!--more-->
+
+The `kubectl drain` command is used to mark a {{< glossary_tooltip text="Node" term_id="node" >}} as going out of service. 
+When executed, it evicts all {{< glossary_tooltip text="Pods" term_id="pod" >}} from the {{< glossary_tooltip text="Node" term_id="node" >}}. 
+If an eviction request is temporarily rejected, `kubectl drain` retries until all {{< glossary_tooltip text="Pods" term_id="pod" >}} are terminated or a configurable timeout is reached.