It's widely accepted there have been three 'waves' in the coffee industry. The first wave of coffee was marked cheaper, accessible coffee that can be changed with milk or sweeteners. The second wave refers to the period where coffee began to be viewed with a unique lens of flavors, where coffee could taste different depending on how it was roasted.
The third wave of coffee is the most recent movement or wave. It's highlighted by a movement to better understand and appreciate higher quality coffee through education, better growing practices, and processing tactics that lead to a better product. Sometimes it's used synonymous with specialty coffee, though the terms are technically different.