# What is precisely a Yangian symmetry?

The terms Yangian and Yangian symmetry appear in a list of physical problems (spin chains, Hubbard model, ABJM theory, $\mathcal{N}= 4$ super Yang-Mills in $d=4$, $\mathcal{N}= 8$ SUGRA in $d=4$), seem to be linked to (super)conformal symmetries and dual (super) conformal symmetries and Hopf algebras.

So, what is precisely a Yangian symmetry, and what is the physical signification of this symmetry?