1955 penny error?

Found this is it worth any thing, worth keeping? What's this error called?

 

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Possible retained cud. See if you can match it up.
http://cuds-on-coins.com/lincoln-cent-retained-cuds-1955/

 

Is it worth putting it in a card board holder? Thank you for the information cud error....

 

You mean a 2x2?
Sure.. why not?

 

Yes, keep it, it's a good die error, the die was cracking up.

 

Is there a proper term for something like this. Die crack or retained cud? Are both terms correct?