What's an actual literal cult?

When I went to the Quantified Self conference in Amsterdam last year, I heard the allegation that Quantified Self is a cult after I explained it to someone who lived at the place I stayed for the weekend. I also had to defend against the cult allegation when explain the Quantified Self community to journalists. Which groups are cults depends a lot of the person who's making the judgement.

There are however also groups where we can agree that they are cults. I would say that the principle applies to an organisation like the Church of Scientology.