"Reason for being" refers to the purpose or meaning behind someone or something's existence. There are several synonyms that can be used interchangeably with this phrase, such as "raison d'être," which is a French phrase that translates to "reason to be," and "purpose," which is the intended use or reason for which something is created or exists. Other synonyms include "mission," "goal," "objective," "function," "duty," and "responsibility." Each of these words implies that there is a specific reason or intention behind someone or something's existence and that a certain function, task, or mission must be fulfilled to serve its purpose.