I haven't been involved in abstract math in close to a decade, but I think it's a description of the (general) inner product. So, a generalization of the dot pr

I haven't been involved in abstract math in close to a decade, but I think it's a description of the (general) inner product. So, a generalization of the dot product. The classic dot product is that operation with the identity matrix. My understanding is that using matrices that way is very common in physics.