Grand Solar Minimum
A Solar "Grand Minimum" is an extended period during which our sun's activity (sunspots, solar flares) diminishes and the energy coming from the sun drops. This resulting in drastic climatic and geophysical changes to all planets our system. These include increased susceptibility to galactic cosmic rays, heightened seismic activity and volcanism, and shortened growing seasons; the latter often results in a global reduction in temperatures (see "the year without a summer").
For a more full appreciation of how it can manifest, see Grand Solar Minimum Symptoms.
Here is a quick video I did introducing the science behind these larger solar cycles (DTube) or: