It is a name for a web directory that appears on sites usually created with WordPress taking advantage of some vulnerability, and is used by hackers and crackers to enter the administration of the site without the need for access keys. The name is formed by 'alpha' (which appears to be the identification of the hackers who created the exploit) 'cgi' (a common acronym on websites for Common Gateway Interface or also for computer generated imagery) 'api' (a common acronym on websites for Application Programming Interface).
