No, I am talking of this phrase which is coming into vogue because lots of people, specially freelancers are carrying on multiple careers as "HR Manager/Photographer" The slasher in 'slasher careers' refers to the "/" symbol between the two careers. And its a progression of the portfolio careers that Charles Handy has spoken about.
I personally think new careers will emerge at the intersection points of careers/functions.
As this article says:
While a new vocation may begin as a hobby, slashers tend to view all their pursuits as careers; and while those who moonlight might quietly take on a second job, career slashers are generally open about their multiple interests. They may even have a business card to prove it: The Wall Street Journal recently ran an article about the increased demand by career slashers for more than one business card so they can effectively promote their varied interests.Check this book by Marci Alboher
Slashers typically have a primary vocation, but they may pursue several other interests over the course of their working lives. For example, someone might be a copyeditor/aerobics instructor for a few years, and transition to a copyeditor/masseuse. As Marci Alboher, who coined the term, said in an interview with BusinessWeek, “Being a “slash” is a way to evolve without giving up the security of a job or losing the confidence in your expertise.”
The Blog that she used to write for the New York Times and the blog she writes at Amazon.