[stephenr]

It literally means a person who purchases something.

No sane person on the planet would consider a person using a search engine for free, "the customer". The customer is the person who buys something - in Google's case, advertising.

[shawnz]

Right, and users of the engine aren't using it for free. They're paying in ad impressions.

[stephenr]

Ad impressions are like shares. They're only valuable if someone is actually paying real money for them somewhere.