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The variables used in general relativity to describe the shape of spacetime. If your question is about metric units, use the tag "units", and/or "si-units" if it is about the SI system specifically.

The metric tensor is a second rank (specifically, it is a (2,0) tensor) tensor $g_{\mu\nu}$ such that $g_{\mu\nu}=\hat e_\mu\cdot\hat e_\nu$. It therefore describes the angles between vectors. Curvature tensors can be derived from it.

This tensor is commonly used in , where the curvature of spacetime describes the strength of gravity, in a sense. A solution to the Einstein Field Equation is a solution for the metric tensor.

The metric tensor formulation is of course, a second-order formulation. The first-order formulation uses the vielbin.

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