CPPM (or PPM as it's sometimes called) allows all the channels from your radio control receiver to be output on a single connector to your RC plane or multirotor's flight controller.
There can be a bit of a problem however, when using CPPM and the FrSky receivers. Because they operate with a short frame-length (about 18mS), not all of the 8 channels will fit and that can cause weird things to happen in radios that always transmit 8 channels.
However, if you're only using 5 of those 8 channels, you can avoid having to reflash your receiver with new software (to produce a longer frame) by making sure that the 3 unused channels are set to output the shortest possible pulse.
Each radio will differ in how this can be achieved. The Taranis allows you to simply transmit only the first 5 channels but many other radios may only offer a fixed number of channels so you'll have to pre-set channels 6-8 to the shortest possible pulse.
If there's a demand, I'll show folk how to reflash these receivers anyway -- just in case you want to use all 8 channels.