Basics
Ad network
An ad network is a company that aggregates ad space from many publishers and resells it to advertisers, usually in packaged bundles and often with its own pricing and targeting.
Ad networks were the first big middlemen of online advertising. In the late 1990s and 2000s, networks bought or represented space on thousands of websites and sold it to advertisers as audience packages ("sports fans", "women 25–34") so buyers did not have to deal with each site individually. Google AdSense is the best-known example on the web; AdMob, Unity Ads and AppLovin play a similar role in mobile apps.
Networks differ from an ad exchange in how they trade. A network typically sets prices and bundles inventory, and may mark it up; an exchange runs open auctions between many buyers and sellers. Today the line is blurred, as most networks also bid through real-time bidding and many exchanges offer packaged deals.
For publishers, networks are an easy way to monetise without a sales team. For buyers, the trade-off is less transparency about exactly where ads run, which historically made some networks conduits for remnant inventory, traffic arbitrage and ad fraud.
Think of it like this
An ad network is like a wholesaler who buys produce from hundreds of small farms and sells it to supermarkets in mixed boxes.
An example
A small travel blog in Portugal joins an ad network that pays it 68% of revenue; the network sells the blog's audience alongside 20,000 other sites as a "European travellers" package.
Related terms
Ad exchange
An ad exchange is a digital marketplace where buyers and sellers of ad impressions meet and trade through automated auctions, usually in real time.
SSP (supply-side platform)
An SSP (supply-side platform) is software that publishers use to sell their ad inventory automatically to many buyers, running auctions and managing prices, deals and quality controls.
Ad mediation
Ad mediation is software that lets app developers connect many ad networks and bidders through one SDK and chooses which network fills each ad request to maximise revenue.
Revenue share
A revenue share is an agreement in which partners split the money earned by an agreed percentage, such as an ad network paying a publisher 70% of ad revenue.
Remnant inventory
Remnant inventory is ad space a publisher has not sold through direct deals, which is then offered through programmatic channels, networks or house ads, usually at lower prices.