Comodality might be the term that less people known, it was introduce in 2006 by the European Comission. It refers to all kind of transportation modes and their ability to be efficient together in order to use resources in an optimal and sustainable way. It's the larger of the three notion exposed here, hence it does take in consideration the fact that modes of transportation are used combined or isolated.
"Combined or isolated", how could comodality be isolated would you said ? Well let's take an example to illustrate this paradox : imagine you have to go to the hairdresser, to reach it you need to take one bus, as usually when you are moving into the city you are using subway, that's what isolated used of transportation in a comodal way is. On the other hand, combined comodality is the use of at least two different modes of transportation between A and B.
Combined comodality definition is close to the notion of intemodality, which is the combination of several modes of transportation on the same journey.
So what is left to define multimodality ? Well, multimodal refers to resources available on one road, between two places. To be clear, if I want to go from Paris to London, what are my choices ? Rail or air, so this is a multimodal road. In opposition, if I want to go from one small city to another, it's quite sure the only way will be the road, so this is not multimodal.
Those notions all include the need of interconnections between transportation operators, here again we can speak about two different kind of interconnection : by node or flew.
Interconnection by node is when connections are made on the same place between at least two modes of transportation. Interconnection by flew go a bit further, it is build on a multitude of interconnections between transportation, very often an infrastructural node plus the imbrication of different networks and all their resources. As an example you can check Karlsruhe tramway, where you can see a clearly every connections.
Hope we made it a clear, and to read your feed backs soon