Here's the super-summarized story for those who are out of the loop: the Bitcoin community has been fighting for years over what they call the "block size increase." From its original design, Bitcoin has capped each block to 1MB, which effectively caps the transactions per second to 4 or so. Raising this limit would allow more transactions per second onto the network, but with the downside of making nodes in the Bitcoin network more costly to operate. The majority of current Bitcoin developers do not want to raise this cap. However, a large group of users and several of the earliest developers (including Gavin Andresen, the guy hand-picked by Satoshi Nakamoto) do want to raise it. There is evidence that Satoshi himself thought that the cap should someday be raised.
There was recently a compromise struck among the largest bitcoin exchanges and mining pools. It was called the Silbert Agreement, or New York Agreement, or Segwit2x. The agreement was to deploy a feature upgrade that the current developers had been pushing (called Segwit) alongside a block size increase from 1MB to 2MB. It broke a stalemate in which the big blockers had been preventing Segwit from going live, and the Segwit supporters had been refusing to increase the block size.
The deal was that Segwit would go live immediately, and several months later, the block size increase would go live. Segwit did go live as agreed, but then its proponents refused to honor the rest of the agreement (since they already got what they wanted).
That was a few days ago, and now we're seeing the backlash: lots of users and capital fleeing to "Bitcoin Cash," a separate branch that recently forked off from the traditional Bitcoin. Proponents (including Gavin Andresen) consider this new branch to be the true Bitcoin, because it's willing to scale with user demand as Satoshi Nakamoto intended. Opponents consider it to be an altcoin that's fraudulently calling itself Bitcoin, since its block size increase is a departure from the original spec.