[Bambora] What is «MD5 Key»?

It is mentioned here: developer.bambora.com/europe/shopping-carts/shopping-carts/magento2#mandatory-configurations

bambora-mandatory--md5-key

A post was split to a new topic: [Bambora] How is «MD5 Key» used?

See also: [Bambora] Where is «MD5 Key» in the merchant interface?