Well it could be a guerrilla or a partisan too. A terrorist TERRORISES ie his aim it to frighten the population in order to get his point across (eg to affect a change policy). A freedom fighter/guerilla/partisan would be an irregular soldier but who fights the forces of the establishment the aim being to win at the end by a series of tactical strikes in the form of assymetric warfare.
Terroists use strikes to not always achieve tactical victories but strategic wins. Terrorists in Mumbai killed many people but they had no hope in hell to keep the hotels they occupied, the military came along and wiped them out winning back those areas. The terrorist aims were to frighten or destabilise society. On the other hand guerillas may have occupied a military base in the hope of holding onto it and not having it relinquished to government forces, see Tiger Tamils.
This can overlap of course. In Afganistan Taleban guerrillas fight NATO forces but elements of the Taleban also detonate bombs in busy marketplaces to terrorise the civilians. Freedom fighter the former, terrorist the latter.