Any interconnected set of nodes such as the electric power network or a communications network.
"The Grid" is a nickname for Internet2. See Internet2
In a vacuum tube or gas-filled electron tube, the grid is a perforated electrode through which electrons may pass. The term typically refers to the control grid in a triode, tetrode or pentode vacuum tube. In these cases, the grid is used to control the amount of current flow between the cathode and plate (anode). As the voltage potential is varied on the control grid, the amount of current allowed to pass through also varies. Relatively small fluctuations in the grid's potential can control substantially larger amounts of current flow through the tube. This phenomenon is referred to as "gain." Tetrodes and pentodes use additional grids to regulate current flow and effect gain. See screen grid
and suppressor grid