HOTP stands  for HMAC based algorithm for a time of passwords. It is an algorithm for generating one-time passwords (OTPs). It is based on the HMAC (Hash-based Message Authentication Code) algorithm and generates OTPs based on a counter that is incremented each time the OTP is used. HOTP is an extension of the TOTP algorithm and has been adopted as Internet Engineering Task Force (IETF) standard RFC 4226.