A microgrid is essentially a localized power grid. The microgrid concept competes with the idea of a traditional large-scale electrical grid serving many thousands of customers.
Techopedia explains Microgrid
In the past, large-scale electrical grids had served many citizens of modernized first-world countries. The idea was to run electricity on an economy of scale, where a massive amount of power supplied by either nuclear, coal or other energy sources would provide large communities with the electrical energy that they needed.
Today, the idea of a microgrid is gaining a lot of traction. One aspect of this is the conflict between the traditional energy sources used in large-scale electrical grids and the new renewable energy sources that sometimes work better closer to the point of origin. The best example is solar energy. Today, more houses and buildings are connected to small local solar energy grids that may only serve one property. However, as solar technology comes down in price and becomes more feasible, some properties can actually benefit from a smaller economy of scale — simple solar cells placed in available areas can take in free natural sunlight and convert it to electrical energy to run a particular set of appliances, or heating and cooling systems.
The idea of a microgrid is changing how we view energy infrastructure. One very common example is the idea that, in large-scale systems, a single line disruption, such as a downed tree, can knock out power to dozens or hundreds of properties, whereas in localized energy grids, repair involves fixes much closer to the actual property and may be more transparent to those who are relying on that energy.