The term 'geometry prefix' refers to a set of prefixes used in mathematics to denote the number of sides or angles of a particular shape. The two prefixes given are 'deca' and 'octa, ' which both have four letters. 'Deca' is derived from the Greek word for ten, and it is used to refer to shapes with ten sides or angles. 'Octa' is derived from the Greek word for eight, and it is used to refer to shapes with eight sides or angles.