Create pod eviction concept and glossary entries

- Created glossary entries for manual and kubelet eviction
  - Created node-pressure-eviction.md and api-eviction.md
  - Merged content from eviction-policy.md and out-of-resource.md
  - Added note to kube-scheduler about node conditions
  - Deleted eviction-policy and out-of-resource.md
  - Redirected old topics
  - Change topic weights

content/en/docs/reference/glossary/api-eviction.md

@@ -0,0 +1,22 @@
+---
+title: API-initiated eviction
+id: api-eviction
+date: 2021-04-27
+full_link: /docs/concepts/scheduling-eviction/pod-eviction/#api-eviction
+short_description: >
+  API-initiated eviction is the process by which you use the Eviction API to create an
+  Eviction object that triggers graceful pod termination.
+aka:
+tags:
+- operation
+---
+API-initiated eviction is the process by which you use the [Eviction API](/docs/reference/generated/kubernetes-api/{{<param "version">}}/#create-eviction-pod-v1-core)
+to create an `Eviction` object that triggers graceful pod termination.
+
+<!--more-->
+
+You can request eviction either by directly calling the Eviction API 
+using a client of the kube-apiserver, like the `kubectl drain` command. 
+When an `Eviction` object is created, the API server terminates the Pod. 
+
+API-initiated eviction is not the same as [node-pressure eviction](/docs/concepts/scheduling-eviction/eviction/#kubelet-eviction).

content/en/docs/reference/glossary/node-pressure-eviction.md

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+---
+title: Node-pressure eviction
+id: node-pressure-eviction
+date: 2021-05-13
+full_link: /docs/concepts/scheduling-eviction/node-pressure-eviction/
+short_description: >
+  Node-pressure eviction is the process by which the kubelet proactively fails
+  pods to reclaim resources on nodes.
+aka: kubelet eviction
+tags:
+- operation
+---
+Node-pressure eviction is the process by which the {{<glossary_tooltip term_id="kubelet" text="kubelet">}} proactively terminates
+pods to reclaim resources on nodes.
+
+<!--more-->
+
+The kubelet monitors resources like CPU, memory, disk space, and filesystem 
+inodes on your cluster's nodes. When one or more of these resources reach
+specific consumption levels, the kubelet can proactively fail one or more pods
+on the node to reclaim resources and prevent starvation. 
+
+Node-pressure eviction is not the same as [API-initiated eviction](/docs/concepts/scheduling-eviction/api-eviction/).

content/en/docs/reference/glossary/pod-disruption.md

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+---
+id: pod-disruption
+title: Pod Disruption
+full_link: /docs/concepts/workloads/pods/disruptions/
+date: 2021-05-12
+short_description: >
+  The process by which Pods on Nodes are terminated either voluntarily or involuntarily.
+
+aka:
+related:
+ - pod
+ - container
+tags:
+ - operation
+---
+
+[Pod disruption](/docs/concepts/workloads/pods/disruptions/) is the process by which Pods on Nodes are terminated either voluntarily or involuntarily. 
+
+Voluntary disruptions are started intentionally by application owners or cluster administrators. Involuntary disruptions are unintentional and can be triggered by unavoidable issues like Nodes running out of resources, or by accidental deletions.