It loosely refers to Roman Catholics who reject the interpretation of the Second Vatican Council as being as re-set or rebirth for the Church and adhere to the worldview that more-or-less defined Catholicism before the council.
I think that anybody who holds to the view that Vatican II was a re-birth for the Church has already separated themselves from the Catholic Church since this is an impossibility for the Church of Christ. It’s not just traddies who should be rejecting such a view, it’s everybody. That’s what’s slowly been happening in the last 20 years, and much more so in the last 5 years at a quicker rate. Slowly traditionalism is being vindicated. Sadly, many still believe (as most believed 40 years ago) that Vatican II made a new Church. One hears it in phrases such as “Vatican II did away with that”, apologies for the Inquisition and the Crusades and other such things (cliche or not). It’s also very apparent, unfortunately, in a complete lack of reference, knowledge and reverence for anything that happened before the the council. Hence the lack of references in much of mainstream Catholic information/pastoral letters/Catechisms to previous councils or the great Doctors of the Church (Aquinas is a small exception, he is casually mentioned every so often, but otherwise we hear nothing of St. Alphonsus, et al).
Catholics are slowly starting to “get it”. If they want to belong to the Church now; they have to acknowledge that it existed before 1965 - and not only existed, but flourished as one and the same institution founded by Jesus Christ.
People are also slowly waking up to the contradictions in the apologetics for the great flourishing that was meant to happen by Church leaders desperately trying to conform the Church to the world. On the one hand, we have those who say that the post-Vatican II period has been a failure only because of the social and political situation in which the Church found herself in. This answer, however, doesn’t account for the promise that was made - namely, that the council would be conforming to the world in a new way; that is to say, that it would try to remodel the Church precisely so to conform to the changing world! So this response hardly works. On the other hand, we see those who say that the post-Vatican II period has been a massive success. To this one can hardly think of a way to respond, since the statistics, experiences and facts simply show the opposite to be true - we simply must admit that there is a massive crisis.
The only solution is to take the position of the ‘traditionalist’ (which does not refer to the SSPX) and say that there is a crisis, and the way to get out of it is to stop trying to make this Divine Institution a worldy-institution (which leads to banal liturgical practice, false-ecumenism, “social justice” with no mention of Christ, indifferentism, abuse scandals etc). That is all the traditionalist is trying to do. We are not trying to reset the clock. That would be a fools game. We are carrying on as normal, within the Church, as fully informed Catholics armed to the teeth with faith, hope and charity. Let the world understand once again that the Catholic Church is the Mystical Body of Christ, founded by Christ and the only Church of God. There will come a time when the Ecclesia Dei Commission is no longer necessary; it will become redundant. That will be the same time when there are no longer two ‘forms’ of the Roman Rite but one glorious Roman Rite (with respect to the Eastern Rites too) which praises God in all His Infinite Majesty.
Laudetur Jesus et Maria semper Virgo!
Pax vobiscum