what is pruning?
Pruning deletes the blockchain on the fly as it is downloaded. It ensures that some blocks are kept, but then deletes the rest of the blockchain after the blocks become too old. Basically most of the blockchain ends up being deleted, with only the most recent few hundred blocks kept, and the oldest ones are deleted as new blocks are received. The downside is that you won't be able to get any new nodes synced and if the blockchain gets corrupted, you will need to redownload (but not store) the whole thing.
