The latest Office Hours podcast by Dr. R. Scott Clark, Dr. Bob Godfrey and Dr. Mike Horton on the topic of being valiant for Truth is an excellent one, conversing about various practical issues the Church would face if we truly want to be biblical and obey the command of Jude 3.
Here, Dr. Godfrey's definition of heresy is a good definition which would really be helpful. Heresy is used "primarily to describe theological errors so serious that those holding such errors cannot be saved". This is indeed an helpful definition which is based upon the Scriptures. Instead of the tradition-based definition of heresy as defined as those teachings that are condemned by the ecumenical creeds, this definition honors Scripture above tradition and seeks to let Scripture itself define the boundaries of the term "heresy".