This is a word of uncertain origin, probably derived from Greek, which indicates a particular method of interpreting the Hebrew text.
Since Hebrew letters also have a numerical value, gematriya plays on this ambivalence to create associations, equivalences and dissonances. For example: the numerical value of the word echad, meaning “one”, but above all “unique” referring to God, is equivalent to that of ahavah, which means love. Multiple conclusions or consequences are then drawn from these parallels. gematriya is a method used especially in qabbalah and mystical texts.
Source: "Gli ebrei questi sconosciuti" by Elena Loewenthal