If you are thinking about putting some banners on your Web site, realize that most ad networks require between 10,000 and 1 million page impressions per month (so they have enough inventory to sell). Be certain to ask about exclusive or non-exclusive representation. Exclusive may get you more money, but less inventory gets sold; non-exclusive may not make you as much money, but you can use another ad network to fill in any unsold ad spaces.
The difference between an ad network and an ad exchange is that ad networks aggregate ad inventory from publishers and resell it to advertisers whereas in contrast, an ad exchange is a marketplace where publishers and advertisers can find and execute advertising transactions, similar to what happens on a stock exchange.
NetLingo Classification: Online Marketing