A systematic shift in technology that changes and improves the way that business is done, while creating new businesses across all industries in the economy.
The first industrial revolution is the typical, steam-engine powered one. The second one comes about 1870 after a lull/plateau in production, and includes:
The third one is computers and the internet, up to and including smartphones.
The fourth one is supposed to be coming, according to some economists, including stuff like AI, blockchain, bioimplants, etc.
Some economists talk about first revolution parts a and b, and second with two parts as well instead of 4.
Rephrasing of this EE video.