Is this a type of rim error?

I am still new to coin collection. I found this kennedy half that the rim doesn't look right. The lettering is still normal( especially on the word dollar and the date and trust on the front) but under the lettering is a ridge. I didn't know if this is considered a type of mint error. Thanks for the help.

 

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Looks like a conventional case of die deterioration in which a ridge forms just inside the design rim.

 

or it was encased in something.... like a good luck keychain maybe?