Definiton 1

Powergrid is one of the two basic ship resources along with CPU used to fit modules on a ship, POS or Dropsuit . Modules intended for larger ships typically require substantially more 'grid.

Definition 2

"The grid." Space in EVE is invisibly divided up into smaller sections called grids. A typical grid might be a sphere with a diameter of 250-350km, but its size and shape can be manipulated by players.