What are Braxton Hicks contractions?

This is what I read about Braxton Hicks which I started searching through babycenter.com which explains about it.

"Braxton Hicks contractions are sporadic uterine contractions that start about 6 weeks into your pregnancy, although you won't be able to feel them that early. You probably won't start to notice them until sometime after mid-pregnancy, if you notice them at all. (Some women don't.) They get their name from John Braxton Hicks, an English doctor who first described them in 1872.

As your pregnancy progresses, Braxton Hicks contractions tend to come somewhat more often, but until you get to your last few weeks, they'll probably remain infrequent, irregular, and essentially painless."