It’s a military term.  “Any locality, or area, the seizure or retention of which affords a marked advantage to either combatant.”  In other words, key terrain is important.  Key terrain has value, both to the one who owns it and to another who would like to own and occupy it.  My idea of real estate agency involves helping buyers find and occupy key terrain at the least possible cost.  If you’re a seller, then it’s to assist you in obtaining that fair compensation for the key terrain you would convey to another.  After 27 years service with U.S. Marines, I have acquired a sense for the creative acquisition of key terrain, and an equally keen sense for protecting the held value of the same.  I apply these senses on your behalf when it comes to real estate in the North Carolina High Country.  Also, one can easily search for “key terrain” at my website: https://www.keyterrain.com.