What's the name of the texture / design pattern found in the background of this site? http://bohemiancoding.com/sketch/
What should I search on Google to find out similar textures?
It is called a Voronoi (cell/noise) pattern. See:
Image 1: A Voronoi pattern, usinhg Photoshop crystallize. Its often a good idea to trim the corner cells away. And if possible do the cells yourself.
Fun link: A interactive Voronoi pattern click to add new cells.
Edity: this can also be the dual solution of voronoi that is called a Delunlay triangulation.