The word 'warlock' has negative connotations - it can be traced to the old Anglo-Saxon word waerloga, which means liar, deciever, or traitor. It is because of this that many men involved in Witchcraft find the term witch preferable. The term has been used less since the revival of witchcraft in the 1950s, though some male members of the Church of Satan still refer to themselves as warlocks.
A traditional warlock is seen as a wizard or sorcerer who has gained their supernatural power and knowledge through a pact with the Devil or demons. A Devil's pact is not part of modern Witchcraft, which ignores the Devil as a belief of Christianity
The TV show Charmed shows a large array of warlocks - their definition seems to be that if a man has an evil looking beard and moustache, can do some motion to indicate 'insert special effects here', and stares pensively through a window, then he is one. Modern day warlocks are so easy to identify.