PPC = Cost Effective Advertising
The Difference: Buying ad space on specific sites vs buying specific audience based on highest bidder.
Real time, impression/click-level bidding can re-target site user drop-off from any campaign, along with overlaying the customer behavior of the target audience.
Google Display Network is one of several display networks, but captures about 25% of the display landscape. It is a great way to enter into the display realm, without spending a lot of money.
Programmatic Media Buying is very popular. This is where you utilize an ad server and target websites across all platforms (desktop, tablets & mobile).
3rd Party Publisher with Small & Large Scale Reach by providing an easy way to purchase inventory on a wide variety of local/national websites with various types of targeting. These vendors provide one-stop shops for aligning with a local or niche online category.