Emrich coined the term "4X" ("eXplore, eXpand, eXploit, eXterminate") in his 1993 review of Master of Orion in Computer Gaming World,[1] describing strategy games that involve exploration, expansion, and exploitation of territory, and extermination of opponents.
Emrich wrote, “Quadruple-X - I give MOO a XXXX rating because it features the essential four X’s of any good strategic conquest game: EXplore, EXpand, Exploit and Exterminate.
In other words, players must rise from humble beginnings, finding their way around the map while building up the largest, most efficient empire possible.
Words like EXcite, Experiment and Excuses (to one’s significant others) must be added to a gamer’s X-Rating list.”[2] The actual first use of the term “4X” remains unknown.
Until April 2002, Emrich was a lead designer of Master of Orion 3, which attempted to add a 5th X, eXperience, to the genre.
[5] He was also a professor at the Art Institute of California at Orange County, where he taught Game Design, Prototyping, and Project Management to students — he regarded this as an "official instance of his lifelong passion for teaching".