インターネット上での日付と時刻：タイムスタンプ（定義）

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

      UTC         Coordinated Universal Time as maintained by the Bureau
                  International des Poids et Mesures (BIPM).

      second      A basic unit of measurement of time in the
                  International System of Units.  It is defined as the
                  duration of 9,192,631,770 cycles of microwave light
                  absorbed or emitted by the hyperfine transition of
                  cesium-133 atoms in their ground state undisturbed by
                  external fields.

      minute      A period of time of 60 seconds.  However, see also the
                  restrictions in section 5.7 and Appendix D for how
                  leap seconds are denoted within minutes.

      hour        A period of time of 60 minutes.

      day         A period of time of 24 hours.

      leap year   In the Gregorian calendar, a year which has 366 days.
                  A leap year is a year whose number is divisible by
                  four an integral number of times, except that if it is
                  a centennial year (i.e. divisible by one hundred) it
                  shall also be divisible by four hundred an integral
                  number of times.

      ABNF        Augmented Backus-Naur Form, a format used to represent
                  permissible strings in a protocol or language, as
                  defined in [ABNF].

      Email Date/Time Format
                  The date/time format used by Internet Mail as defined
                  by RFC 2822 [IMAIL-UPDATE].

      Internet Date/Time Format
                  The date format defined in section 5 of this document.

      Timestamp   This term is used in this document to refer to an
                  unambiguous representation of some instant in time.

      Z           A suffix which, when applied to a time, denotes a UTC
                  offset of 00:00; often spoken "Zulu" from the ICAO
                  phonetic alphabet representation of the letter "Z".

      For more information about time scales, see Appendix E of [NTP],
      Section 3 of [ISO8601], and the appropriate ITU documents [ITU-R-
      TF].