In some cases, the specific terminology of certain coaches has made its way into the general parlance. Coaches, having no motivation to publicize their plans, usually adopt cryptic codes for certain positions, using letters, numbers, or short names for their convenience. One set of designations which has been making the rounds, as of this writing on Web sites, purporting to explain football is the letters X, Y, and Z to designate receivers. It is doubtful that many coaches agree on the use of these terms to designate specific positions consistently from play to play, and those letters do not seem to enlighten but only to obscure. (One manual for football spectators, in the 1960s, explained that someone calling offensive plays in the huddle would point to primary, secondary, and tertiary receivers while giving them those letters; those designations would vary depending on the play, not on the positions those receivers occupied.) However, one such letter designation has caught on recently: "H-back", illustrated in the offensive formation below: