One-Time Password (OTP) A security system that requires a new password every time a user authenticates themselves. OTP generates these passwords using either the or . The equivalent term "S/Key" is a trademark of , so the name OTP is used increasingly. See - "The S/KEY One-Time Password System" and - "A One-Time Password System". {(http://www.cs.umd.edu/~harry/jotp/)}. (2000-01-31)