A node (that is a single computer which has a single operating system installed on it) requires one licence, regardless of how many cores the processor has.
multiple nodes across a network can be set up for advanced configurations, where each processing node and each client machine needs a licence. If I machine is being used both as a client machien and a processing node, I understand it only needs a single licence. (there is also a need for a server on the network to coordinate the nodes, but it does not need a licence)
Note that floating licences are more expensive than node locked licences, but node locked licences can still be transfered between computers by deactivating the licences on the first, and typign the licence code into the second.