You know that a power system has a generating unit to produce electrical energy that is consumed at the load. This energy cannot be stored and has to be consumed at the similar instant. But because the load is not concentrated at one place and it is not probable to have a generator extremely close to the load centre at all times, we go for transmission lines that facilitate transmission of power from generator to load. Therefore all generation units and load centers are linked and a grid is formed.
The grid is primary a connection of generating stations, substations and loads by transmission lines, at a voltage level above the distribution voltage. The distribution voltage, thus, is not strictly described. It is different for different areas. In a few distribution systems, power is taken from the grid at 33 kV, in some it is taken at 66 kV and in some; it might even be taken at 220 kV. Thus, the grid covers the above mentioned high voltage system down to the level of linked point of the distribution system.
Definition of a grid
"The high voltage backbone system of inter-linked transmission lines, generating plants and substations" Grid is elaborates in the Electricity Act, 2003.