Islam is the Quran and Sunnah as it was understood and practiced by the Companions. There are groups which use the term "Islam" and "Muslim" yet if you deny any of the 3 above you will have an incomplete Islam (sect) or a new deen altogether such as Qadariyah (deny Qadr), Ahmediyah (who believe in a new prophet), Quranites (who deny the Sunnah), Shia (deny Sunnah, fabricate many things and make takfir of the Companions), extreme Sufis (who do not follow the understanding of the companions, and are known for many innovations), and so on...