It is a practice of adding the numerical values of the letters to finally obtain a single number. He intended to obtain a quality from the words written in Greek. The word as such means counting equal or counting equal. It was a system used by the Greeks to learn mathematics and geometry with pebbles or stones (psephia in Greek means pebble or counting).
Also isopsyphy. Of isos, igual and psephos, pebble, tejuelo that the Greeks used in the calculations. Technique transforming Greek words into numbers by adding the value of each alphabetic character. In this way with a number you could mention someone or something in a cryptic way. In Revelation, some say, John the Evangelist would allude to Nero with the number 666.