[Beowulf] What is rdma, ofed, verbs, psm etc?

[Faraz Hussain]

I have never understood what these acronyms are. I've been involved  
with HPC on the applications side for many years and hear these terms  
pop up now and then. I've read through the wikipedia pages but still  
do not understand what they mean. Can someone give a very high level  
overview of what they are and how they relate to HPC?

Specifically, how does it relate to a simple hello world mpi program  
like this:

http://mpitutorial.com/tutorials/mpi-hello-world/