It stands for "Core Untouched Soft Fork". It is a faster, safer, less-political way of doing soft forks.
BIP300 allows miners to collect more revenue -- potentially.
Soft forks allow people to use Bitcoin in whatever way they like -- growing us to 8 billion users. Miners collect transaction fees from each transaction, so adoption will always improve their bottom line.
CUSF is not something that an individual miner can do. 51% hashrate must do it collectively. So we need a few pools to run the new software. Pools will only do the things that their customers demand! So we must build a small movement, first.
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