A group or set of five...the pentad was a Pythagorean term for the number five. A pentagram, symbol of the pentad, was used as a secret sign to recognize each other. In a passage from Lucian, he refers to the pentagram as the secret sign of brotherhood between the Pythagoreans.
"Over 20 years ago I devised a unique variant on the Bacon Bilateral. Below I describe the cipher and its method of encryption."