Shaper storms are violent reality distorting cataclysms that affect the Coda. They have been going on for centuries. "Cataclysm" is a common vernacular used to describe these events, and no scientific attempt has ever been made to explain them.
The cataclysm is a large-scale world event which happens dynamically when Freelancers embark on expeditions beyond Fort Tarsis. Freelancers can fly into these spacetime storms and appear on the "other side" upon doing so.
It has been indicated that the Cataclysm may be pocket universes of sorts. It has been joked that the Mass Effect setting could fit inside one of them.