The term “adaptogen” was coined by the Russian scientist N.V. Lazrev, back in 1947, when he realized that certain plants contained an unique action to increase resistance to adverse conditions.

There is no “official” definition.   It is stated that it is derived from an herb and that it isn’t a particular mineral or vitamin.  After that it gets a bit foggy.

Probably the best is that an adaptogen is a substance that demonstrates a nonspecific enhancement of the body's ability to resist a stressor.

When a plant had to survive a stressed it develops properties, that are yet to be isolated and labeled.

These plants, when taken into the body, helps the body adapt to the same type of  stressor as the plant had to overcome.