We always come across many CS concepts in our real life.
I will be posting some of these with a preceding string of CS concepts in real time in title.
I am here not to reinvent the wheel nor to teach you the concept itself.
So, please visit this page and have an overall view on the topic before you move ahead : https://en.wikipedia.org/wiki/Dangling_pointer
I happen to be admin to a few groups at Facebook. And most of these groups have a membership process where any facebook user can come and request to join the group.
When such an incident happens, imagine the user account to be an object. Everything else that is concerned with this object, points to the object. Including the requests sent, pictures, invitations and many more.
So, when a request is sent by one such user, and, before the admin approves it the user deletes/disables his account, then there is an active request or a pointer to the user object but the user himself doesn’t exist; So, now the request becomes a dangling pointer.