Buying ads on Facebook means taking part in a world wide auction.
The demand for reaching users is greater than the supply of ad space, so you're competing against millions of others all trying to get their message seen. When targeting a segment of Facebook's users, understanding different bidding strategies is key to making sure your ads come out on top.
Take a look at the below infographic from Nanigans for an explanation of Facebook's distinct bid types, how they impact your ad's effective reach, and tips to help you achieve your campaign ROI goals at scale.