The easiest thing for people to do if they aren't confident about their level of stress (moderate vs vigorous vs maximal) is to wear a smart watch with a HR monitor. They aren't perfect (chest straps better yada yada) but you can see your HR zones and if you are in Z1 you are moderate, Z2/3 vigorous.

The language isn't that precise because a trained marathoner is doing 7 minute miles for two hours at 50% of the populations resting heart rate.