You can define text snippets with
#+MACRO: name replacement text $1, $2 are arguments
which can be referenced anywhere in the
document (even in code examples) with
{{{name(arg1,arg2)}}}. In addition to defined
macros, {{{title}}}, {{{author}}},
etc., will reference information set by the
#+TITLE:, #+AUTHOR:, and similar lines.
Also, {{{date(FORMAT)}}} and
{{{modification-time(FORMAT)}}}
refer to current date time and to the modification time of the
file being exported, respectively. FORMAT should be a
format string understood by format-time-string.
Macro expansion takes place during export, and some people use it to construct complex HTML code.