The term "pyramid" is used in two ways in logology: 1) a "word pyramid" is a word ladder in which each step adds a letter -eg, I IN FIN FIND FIEND FRIEND; 2) a "pyramid word" has an abstract 'pyramid' of letter frequencies -eg, REMEMBERER with 1B, 2Ms, 3Rs, 4Es. Both of these misuse the word pyramid to mean triangle. A pyramid is three dimensional -- a polygonal base with triangular sides that meet at a point. The base can have three or any higher number of sides but it's usually thought of as a square because the Egyptian pyramids.
"A True Pyramid,"
Word Ways: Vol. 38
, Article 13.
Available at: http://digitalcommons.butler.edu/wordways/vol38/iss4/13