Alert rules Condition

I'm looking through the azure condition options.

One of the options is  "Checks Failed Percent".  It's an azure alert rule on a VM (Metric)

Can't find any data online, what will trigger the rule?

Let's say I have it like this: Whenever the average check failed percent is greater than 2%

What will trigger the rule? Is it when the CPU and Ram hit X % of CPU usage?

Anyone got a link, where you can read about all the conditions ?