According to the dictionary, a flywheel is:

"a heavy disk or wheel rotating on a shaft so that its momentum gives almost uniform rotational speed to the shaft and to all connected machinery."

Ref: https://www.dictionary.com/browse/flywheel

In the technology industry, founders and investors like to talk about "flywheel effects" in their business models, which are effects that increase their growth momentum.

In his book Good to Great, Jim Collins defined a flywheel effect as:

"In building a great company or social sector enterprise, there is no single defining action, no grand program, no one killer innovation, no solitary lucky break, no miracle moment. Rather, the process resembles relentlessly pushing a giant, heavy flywheel, turn upon turn, building momentum until a point of breakthrough, and beyond."

Ref: https://www.jimcollins.com/concepts/the-flywheel.html

If we think about trends on social media, someone had to start them and push them until they gathered enough momentum that they started to power themselves through the feeds of many users.

In my opinion, the most impactful examples of the flywheel effect are in social media, when trends, memes, or attacks gather their own momentum when amplified by the algorithms and network effects of those platforms.

The social media platforms are very impactful upon culture, news, or even election results. Sadly, we often see bad or inaccurate information trending on social media: bad news travels faster than good, as it attracts more engagement via rage-bait, and in turn the algorithms reward that engagement with greater reach.

Social media is a powerful flywheel for bad ideas, and once it builds momentum it can be unstoppable.