Original: People who deviate from orthodoxy by professing a doctrine considered to be false are most often called heretics or radicals, while those who deviate from orthodoxy by removing themselves from the perceived body of believers are called schismatics.
Simplified: People who profess a doctrine considered to be false by the majority are most often called heretics. People who separate themselves from the body of believers, i.e. from full communion, are called schismatics.