RTB stands for  Real-Time Bidding and is a form of programmatic ad buying. This is the process of bidding on space sold through publishers through an auction model in an online exchange. In this instance the highest bidder wins, all in the time it takes to load a webpage.
Programmatic marketing, on the other hand, includes guaranteed direct buying, preferred deals and private exchange buying when finding good placements, meaning that you know there will be a place for your ad rather than taking the risk of bidding.
Both have their merits, however, it is worth chatting to an expert programmatic media buying agency such as WebBox to ensure you’re making the right decision for your business.