Gravimetric shear

Gravimetric shear, also known as "grav shear" or "spatial turbulence," is a type of gravimetric distortion and a force commonly associated with certain astronomical phenomena such as stellar clusters and neutronic storms, that can pose a threat to starships. Shear is caused by localized, extreme differences in the gravitational coefficient that produce great stress on matter that crosses the point of localized difference.

The Enterprise NX-01 encountered severe grav shear in 2152 when it passed through a Class 5 neutronic storm. (ENT: "The Catwalk")

Protostar clusters, such as the Argolis Cluster, are generally regarded as impassible to spacecraft due to their intense gravimetric shear. In 2374, Captain Benjamin Sisko planned an attack on a Dominion sensor array through the Argolis Cluster. He was confident that Jadzia Dax, having studied protostar clusters, would be able to navigate the USS Defiant around the gravimetric shear. (DS9: "Behind the Lines")

In 2375, a class-2 shuttlecraft from the USS Voyager was caught in the gravimetric shear from a proto-nebula, necessitating the evacuation of those aboard. (VOY: "Drone")

Later that year, the USS Voyager experienced heavy gravimetric shear from a subspace sinkhole, that had earlier swallowed one of its shuttlecraft. (VOY: "Gravity")