Although a Serial Number is technically also an Activation Key, only a  Serial Number can be used for a product activation.

 

Each Serial Number can be used once (default) but the Maximum Key / ID usage can be changed. This allows to use one Serial Number on multiple machines.

 

In the moment, an Activation Key is used, also an Activation Request is recorded.  An Activation Key can have one or more Activation Requests:

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