Bruce S. Bertram from The Word of God Ministries and http://www.wholebible.com proposes a different definition of a 'cult' than the currently accepted version. Pun intended.
Cults are traditionally defined by somebody's opinion of orthodoxy. The dictionary definition of orthodox is "conforming to the approved form of any doctrine." In other words, orthodox means accepted opinion. Orthodoxy can include the Bible, but usually includes a lot of men's opinions too. If a person or group is lacking in any of the "orthodox" or accepted doctrine or dogma, then in the opinion of the "orthodox" they must be a cult or part of one.
I propose a better definition of orthodox, and of a cult or cultist. My definition of a cult or a cult member is a group or a person who at most gives only lip service to God. Orthodox then would be those who actually do what God says. These two definitions take into account all those who smugly wrap themselves in church or synagogue doctrine, yet have no intention of anything more than lip synching the Word of God. It includes anyone who is in a "religion" and denies the whole truth of the Word. It also gathers up all those part-Bible people who sit in judgment on the Word, picking and choosing what part of it they want to follow. We can throw in all those people with doctrines that are used to separate us from abiding in His living oracles too.