Step-by-step explanation:
The definition of a frontier a border between two countries, or the outer limit of what has been explored.
The border between United States and Canada is an example of a frontier.
When there is a new plot of land that has never been explored, this is an example of a new frontier.
When there is a new scientific theory that has not yet been explored, this is an example of a new frontier.
noun
The border between two countries.
noun
An undeveloped area or field for discovery or research.
Theories on the frontier of astrophysics.
noun
Any new field of learning, thought, etc. or any part of a field that is still incompletely investigated.
The frontiers of medicine.
noun
A region just beyond or at the edge of a settled area.
noun