ISO 8601 is an international standard for representing date and time information. It specifies a format for date and time strings that is widely used in computer systems and on the internet.

The basic format of an ISO 8601 date string is YYYY-MM-DD, where YYYY is the four-digit year, MM is the two-digit month, and DD is the two-digit day. For example, the date March 14, 2022 would be represented as 2022-03-14 in ISO 8601 format.

ISO 8601 also allows for the representation of time information in the format THH:MM:SS, where T is the separator between the date and time components and HH, MM, and SS represent the hours, minutes, and seconds, respectively. For example, the time 1:23:45 PM would be represented as 13:23:45 in ISO 8601 format.

Combined date and time information can be represented in ISO 8601 format as YYYY-MM-DDTHH:MM:SS, with the T separating the date and time components. For example, the datetime March 14, 2022 at 1:23:45 PM would be represented as 2022-03-14T13:23:45 in ISO 8601 format.

Here are some examples of ISO 8601 date/time formats:

  • Date only: 2022-03-14
  • Time only: 13:23:45
  • Date and time: 2022-03-14T13:23:45
  • Date and time with timezone offset: 2022-03-14T13:23:45-04:00
  • Date only with week number: 2022-W11
  • Date with week number and weekday: 2022-W11-1 (Monday)
  • Duration: PT1H30M (1 hour and 30 minutes)
  • Period: 2022-03-14/P1M (period of 1 month starting from March 14, 2022)

Note that the T separator is used between the date and time components in ISO 8601 format, and timezone offsets are represented as a positive or negative offset from Coordinated Universal Time (UTC). The W character is used to represent weeks, with the week number following the W character and the weekday number following the date component with a - separator. Duration and period strings begin with P, followed by the duration or period value and units (H for hours, M for minutes, D for days, W for weeks, M for months, and Y for years).