This question has been asked of me in every interview I have had as I am seeking new employement as an educational leader. My answer is always short and susinct. But I have to say my ideas of professional develpment are constantly changing.
When I first started teaching I use to attend professional develpment one special days or half days. I would be, through this structured activity, encouraged to learn and grow during those times. The porblem was they were never long enough, they never met everyones individual needs and they were always planned by someone who has been out of the classroom for a while, leaving me often wanting so much more.
In the past few years my image of professional development is no longer something that is done on certain days of the year. My professional develpment happens every day, mutliple times a day. I use my google reader and my twitter account to find more resources that I ever would have from a workshop, conference, or half day inservice. Twitter, when used for this purpsoe (and not just following Shaq and John Mayer) is a powerful tool in interacting with other educators around the world. I've grown more and helped students more through these interactions and I'm a better teacher and leader for it.
All thanks to Al Gore for inventing this crazy thing called the internet :-).
To find out more develop your PLN through twitter:
How to build a PLN? from Elena Elliniadou on Vimeo.