Gnosticism, Armenianism, Calvinism, Universalism, Trinitarianism….need I go on? Just take off the ISM, add IST, and you have the practitioner of each particular entry.
You get the point. There are a LOT of ISM'S in the (limitless) world of Christian Theology. I'm convinced most people don't actually know what they mean. They are thrown around by people who have a need to put others into categories – "He believes X-ISM, so he is an X-IST", OR, "He's now in error – he's an (insert your favorite IST-ending word here)". And make no mistake about it – the offending word is probably whispered and the implied brand, heretic, is allowed to hang in the air.
HE will not be pigeon-holed into an ISM – HE is a person who wants a REAL, LIVE, VIBRANT, PERSONAL relationship with each of us.
Not one single ISM brings us any closer to knowing Him better.