When is a gang rape said to have been committed?

IPC Section 376D.  Gang rape: Where a woman is raped by one or more persons constituting a group or acting in furtherance of a common intention, each of those persons shall be deemed to have committed the offence of rape and shall be punished with rigorous imprisonment for a term which shall not be less than twenty years, but which may extend to life which shall mean imprisonment for the remainder of that person's natural life, and with fine: Provided that such fine shall be just and reasonable to meet the medical expenses and rehabilitation of the victim: Provided further that any fine imposed under this section shall be paid to the victim.