Cell walls in lath martensite - Meaning
According to this Wikipedia page:  


  Martensite, named after the German metallurgist Adolf Martens
  (1850–1914), most commonly refers to a very hard form of steel
  crystalline structure, but it can also refer to any crystal structure
  that is formed by diffusionless transformation.1 It includes a class
  of hard minerals occurring as lath- [emphasis mine] or
  plate-shaped crystal grains.


Lath basically means the shape of a woven screen when viewed close up, or like a grid of alternating appearance.