What is the meaning of the term "full-node"? There seem to be some different interpretations of what the term "full-node" implies. E.g. there seems to be some disagreement whether a pruned node is still a full-node.

So: What characteristics must be fulfilled to label a Bitcoin client as a full-node?
Fully validating nodes ("full nodes") are clients that have validated the whole blockchain self-sufficiently and enforce all of the rules of Bitcoin on any data they receive. Therefore, they cannot be cheated by means of invalid blocks or transactions.
Running your own full node is the most secure, most private, and least trusting way to participate in the Bitcoin network. A full node is necessary to prevent invalid blocks when mining.

Common usage of the term does not require that the node keeps all blockchain data at hand. Although many full nodes have a complete copy of the blockchain, full nodes can also run in pruning mode. 

Nodes that can serve the complete blockchain are referred to as Archival Nodes.

Sources: 


The Bitcoin wiki explicitly describes pruning as an option for full nodes (see Wiki: Full Node).
Bitcoin.org: What is a full node?
Bitcoin Core developer Pieter Wuille announced the pruning feature thusly on Twitter:


  @orionwl just merged pruning support in #Bitcoin Core! Run a (no wallet) full node with 1.3 GB storage. Thanks to all who contributed.