It allow to set a UID or User ID other than 0 for Pods or Containers. UID is not a username.
By default containers run as 'root' with UID=0 and GID=0.
$ id
uid=0(root) gid=0(root) groups=0(root)
Two types of Security Context
1. Pod level
Security Context applied to all containers in the Pod.
2. Container level
Security Context applied on a per individual container.
Override Pod level Security Context - Container level Security Context can be override/change the Pod level Security Context.

* runAsUser

* runAsNonRoot

* runAsGroup

* fsGroup - The field defines a special supplemental group that assigns a group ID (GID) for all containers in the pod.
            This group ID is associated with the Volumes (emptyDir) mounted at specific folder path in Container (/FOLDER_NAME/FOLDER_NAME) and with any files created in that volume.
            If the volume type allows this (as emptyDir volume type) the owning GID will be the fsGroup.
            It control access to shared volumes by Containers in a Pod.
            Allows the config of Group ID or GID must match the shared storage GID to have access to that volume.

* allowPrivilegeEscalation

* readonlyRootFilesystem
