Definition - What does Hardy mean?
Hardy is an adjective used to describe any wine grape variety which is resilient to many factors such as harsh climates, diseases, rot, mold and pests. These varieties are typically cultivated where other varieties do not perform well. They may be both red and/or white grapes.
In addition, "hardy" can be synonymous with certain nuances these grapes can impart into a wine.
WineFrog explains Hardy
Hardy is a word used to describe a certain type of wine grape which is resilient in many ways. It may be hardy in the fact that it can maintain its integrity and balance in hot and/or cold climates. A certain wine grape may also be "hardy" in the way it resists rot, mold or certain pests.
For instance, a hardy red variety of grape may be thick-skinned, not only resisting
high temperatures, but also rot in times of high precipitation or
humidity. These grapes may also impart structural character to
wine such as tannin (due to thicker skin development) and levels of aroma and flavor to a wine.
As for white wine grape varietals, they may also be thick-skinned, resistant to intense sun rays and hot and/or cold temperatures. How any grape survives and resists in a "hardy" manner is one which can impart complexity into the wines they are made from.