What does a blue edges in a mesh mean? (pic included)

As per the title what does blue edges in my mesh mean?

Done alot of searching and can’t figure it out. I imported this from 3d Max. Blue edges result was from a mirror modifier and edge extrusions around the arm done in Max. The arm also smooths independently of the rest of the body when auto smooth is turned on. Weird…thanks!

The blue edges are marked as being Sharp https://www.blender.org/manual/modeling/meshes/editing/edges.html?highlight=sharp#mark-sharp-and-clear-sharp

Awesome thanks for that!