Differences between terms: core, cpu, processing element, processor, processing unit, functional unit?

I was wondering what differences are between the following terms: core, processor, cpu (central processing unit), processing unit, processing element, functional unit?

Here are what I have encountered during reading or listening:

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  a functional unit is a ALU or FLU or something else.

  
  


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  a cpu can have multiple cores.

  
  


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  a processing element is mentioned in texts without defined. Is it the same as a core?

  
  


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  The names of a cpu and a processing unit only differ in "central", but since a functional unit is part of a cpu, I am not sure if a processing unit is just part of a cpu also.

  
  


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  my guess is a processor and a cpu are the same?

  
  

If the names are meaningless, how many different concepts are represented by those terms actually, and what are they?

Thanks.