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Why are some deep linear seafloor features called trenches even though they are not subduction zones?

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World map highlighting major features of the ocean basins, including trenches, ridges, basins, and plateaus labeled throughout the Pacific, Atlantic, Indian, Southern, and Arctic Oceans. Continents are shown with shaded terrain, and prominent undersea features such as the Mid-Atlantic Ridge, Mariana Trench, and Kerguelen Plateau are marked across the map. — ocean basin Major features of the ocean basins.

While the term "trench" is most commonly associated with subduction zones—where dense oceanic plates descend into the Earth's mantle—some deep, linear seafloor features are labeled as trenches despite having different geological origins.12

These features are named based on their physical appearance as deep, narrow troughs, but they are formed by distinct tectonic processes:

Fracture Zones: Some features, such as the Vema Trench located on the Mid-Indian Ridge, are actually fracture zones. These are linear breaks in the seafloor created by the movement of tectonic plates.1
Rift Valleys: The Diamantina trench is classified as a rift valley. It formed due to extensional forces when Australia and Antarctica separated millions of years ago, rather than through the convergence of plates.1
Unknown Origins: Other features, such as the Vityaz Trench near Fiji, are identified as aseismic (inactive) troughs, though their specific geological formation remains unknown.1

In summary, while these features share the "trench" designation due to their morphology, they lack the subduction-related dynamics that define typical deep-sea trenches.1