The phrase "solar activity" refers to the things that happen on the Sun, such as explosions called solar flares, bursts of solar wind, or changes in its magnetic field. Full definition
There are very good correlations between solar activity and temperature, which could account for some, or perhaps all, of the observed climate change. (dotearth.blogs.nytimes.com)
Those are paced by orbital variations, which have nothing to do with solar activity. (realclimate.org)
Since the 1940s and up to 10 years ago we have had the highest solar activity in 1000 years. (climatedepot.com)