Watchman Fellowship usually uses the term cult with a Christian or doctrinal definition in mind.
Generally it refers to witchcraft, satanism, neo-paganism, or various forms of Psychic discernment (astrology, seances, palm reading, etc.). New Age is a recent and developing belief system in North America encompassing thousands of autonomous (and sometime contradictory) beliefs, organizations, and events.
It is based on a farming term in Latin meaning cultivation.
Sociologists and anthropologists sometimes use the term cult to describe religious structure or belief patterns with meanings (usually non-pejorative) unique to their disciplines.
In addition to these usages, Christians generally have a doctrinal component to their use of the word.