In the February 1992 Word Ways, Christopher McManus introduced the concept of halfway words: trios of words where every letter in the middle word is midway in the alphabet between the corresponding letters in the end words (for example, AGE-JIG-SKI, where J is halfway between E and I).
Word Ways: Vol. 25
, Article 3.
Available at: http://digitalcommons.butler.edu/wordways/vol25/iss3/3