Most "modes" like AM/FM and maybe SSB are like physical layer protocols, essentially just modulation schemes. A number of digital modes also maybe fall into th

Most "modes" like AM/FM and maybe SSB are like physical layer protocols, essentially just modulation schemes. A number of digital modes also maybe fall into this category as well as morse. FT8 is more of an application layer technology. It uses frequency shift key as it's physical layer but also has other abstractions at work like error correction and some session state management. It's not the only mode that could be described this way either, just the most popular right now.