The Concise Oxford Dictionary defines apostasy as
1 Renunciation of a belief or faith, esp. religious
2 abandonment of principles or of a party
3 an instance of apostasy
And apostate as
a person who renounces a former belief, adherence etc.
The root of the word is APO- Away from, and -STAT stand.
So as link rightly pointed out, all JW's that converted from other religions are apostate to their former belief. This is a word, like "Truth", that has been hijacked by the WTBTS and imbued with all sorts of overtones and associations not present in its correct meaning. They have turned "apostate" into meaning some sort of bogeyman, a bit like FredHall's picture.
It is an excellent mechanism for stopping JW's from considering opposing viewpoints and arguments.
I remember how well conditioned I still was some years after I had escaped the bOrg. As I entered sites in the "Jehovahs Witnesses - Opposing Views" category, my heart was pounding - this was APOSTATE!!! Glad I found you all!!