It is a traditional russian weight training tool.
http://en.wikipedia.org/wiki/Kettlebell
Oh and I whipped out my book by Pavel (who is considered the authority on kettlebells in America). For the average woman, he recommends starting with 18 lbs, for a strong woman (who has been working with weights), he recommends starting with 26 lbs.
I personally started with 15 lb because kettlebells made me a little nervous but realized quickly that it was too light and used 20 lbs but now I mostly use 25 and a 35 lb kettlebell. I will also sometimes use a 45 lb kettlebell for 2 hand swings.