Substitution variables are a powerful capability for some clients like Jira to customize the creation or updating of issues using values from issues or other Jira information. Variables provide text string representations of fields useful for inclusion in other fields - see Substitution Variables for Jira for more information. For other clients, there are more limited capabilities that follow the same general technique.
The syntax for referencing substitution variables is: %<variable name>%.
Substitution variables and variable replacements
Variable Replacements are different than substitution variables. Don't confuse them or their uniquely different syntax.
Configured date format
For date substitution variables, the format of the replacement variable can be specified if the default format is not desirable. The format is specified by a Simple Date Format string enclosed in parenthesis following the substitution variable name. For example: %now(yyyy-MM-dd)% will result in replacement like 2019-11-08.