What’s an inverted yield curve?

With some much talk about an upcoming recession, there’s been quite a bit of focus on short verse long term bond yields. Investors have decided there’s immediate risk in the markets and are willing to take lower yields/profits for longer term investments. Usually it’s the opposite, which signals concern in the institutional investing world.
Entailed is great read on the inverted yield curve issue:

https://www.nytimes.com/2018/06/25/business/what-is-yield-curve-recession-prediction.html?module=inline