In Internet advertising jargon, an "impression" is defined by Wikipedia as
the display of an ad to a user while viewing a web page.
The word is most often used in the term Cost-per-Impression (CPM), the amount of money an advertiser spends for every 1000 views.
According to Reference.com, "impression" is defined as
the first and immediate effect on an experience or perception of the mind
What does the word "impression" have to do with Internet Advertising?
Who coined the term, and how did it come about?