In a paper I am working on, I come across a term called  "graph canonisation "


According to [math-world Wolfram](http://mathworld.wolfram.com/CanonicalLabeling.html): 


>A canonical labeling, also called a canonical form, of a graph $G$ is a graph $G^{'}$ which is isomorphic to $G$ and which represents the whole isomorphism class of $G$ (Piperno 2011). The complexity class of canonical labeling is not known

Could one elaborate on that ?

**Motivation** : I am working on graph isomorphism [(See this paper by E.M Luks)][1].


  [1]: http://ix.cs.uoregon.edu/~luks/CanLabel.pdf