hCalendar (short for HTML iCalendar) is a microformat standard for displaying a semantic (X)HTML representation of iCalendar-format calendar information about an event, on web pages, using HTML classes and rel attributes.
It allows parsing tools (for example other websites, or browser add-ons[1] like Firefox's Operator extension) to extract the details of the event, and display them using some other website, index or search them, or to load them into a calendar or diary program, for instance. Multiple instances can be displayed as timelines.