# Is it possible to define and refer to constants in MediaWiki?

Is it it possible in MediaWiki to define a constant and then include the constant in other pages?

E.g. could MY_HELP_MESSAGE be defined as If you want help, contact help@somedomain… and MY_HELP_MESSAGE be called via e.g. {{MY_HELP_MESSAGE}} (as per https://meta.wikimedia.org/wiki/Help:Variable)?

Yes. Use vardefine.
#vardefine