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


According to math-world Wolfram : 


>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