This surah is called Surah al-Fatihah either because fo it being the opener of the Al-Qur'an starts with this Surah or because of it being the opener of Salah, as Salah also begins with the same surah. Fatihah is an Arabic word, which means the opener or beginner. Our of all the surahs of Al-Qur'an, Surah al-Fatihah was the first surah which was revealed as a complete surah whereas other surahs were revelaed piecemeal.