Spektrum "serial" receivers?

I am a Spektrum (DX8G2) user about to embark on my first race quad build (Alien) and am looking at my receiver options. I have somewhat settled on the SPM4649T:

https://www.horizonhobby.com/spektrum-dsmx-quad-race-serial-receiver-with-telemetry--p-spm4649t


But wanted to clear up a terminology issue since I am still with much to learn. In information about this rec. and others,,,call it a one wire serial receiver. Is the term "serial" Spektrum's way of saying PPM/CPPM? Just curious. I understand the latter terms but do not understand what serial means.

Any help would be very appreciated. Thanks all in advance