Programmatic (also known as Programmatic Buying, Programmatic Ad-Buying, or Programmatic Advertising) is the buying and selling of online media through automated systems (AdTech platforms).
The opposite of programmatic media-buying is manual media-buying, whereby ads are bought and sold with human interaction (via salespeople).
While there still may be some human element involved in the process, most of the media buying and selling is done in an automated, or programmatic, fashion.
There are many different types of programmatic media-buying, such as Real-Time Bidding (RTB), Programmatic Direct, and Private Marketplace (PMP).