Linked from
The 21 pages that link to Dual space, each with the reason it gives.
TensorRelated: Covectors are elements of this space and provide tensor inputs.
Distribution theoryRelated: Distribution spaces are continuous duals of test-function spaces.
Support functionRelated: Support functions are naturally defined on the dual space.
Eberlein–Šmulian theoremRelated: Weak convergence is defined by testing against this space.
Bra–ket notationRelated: Bras belong to the dual space associated with the ket space.