Braxton Hicks contractions are random, patternless uterine contractions that start early on in pregnancy. They are referred to as contractions because they technically are, but they have nothing to do with labor contractions. Braxton Hicks contractions are generally painless and normally hardly even noticeable. Your uterus will feel firm during a Braxton Hicks contraction, but they normally pass with a simple change of position.
Braxton Hicks contractions are, as you probably guessed, named after the doctor who first observed and documented them the English doctor John Braxton Hicks. Although not every pregnant woman notices Braxton Hicks contractions, everyone has random uterine contractions. Braxton Hicks contractions are commonly noticeable from the later part of the second trimester of pregnancy up to the time you give birth to your baby, though they start at around the sixth week of pregnancy. Describing contractions accurately is very difficult, but when you get Braxton Hicks contractions you will know for sure. They don't feel anything like labor contractions, and are characterized by a sudden tightening of your growing uterus. Have you notice how your belly will go rock hard all of a sudden, only to go back to normal a few seconds later? Those are Braxton Hicks contractions. And excuse me for giving too much information, but Braxton Hicks contractions are extremely common after a woman has experienced an orgasm.
Later in pregnancy, these uterine contractions become more frequent and sometimes even painful. It can be hard to distinguish Braxton Hicks contractions from the real thing around your due date, but there is one clear difference: labor contractions get closer together and follow a definite pattern. They also get longer as the birth draws near, and get more painful. Braxton Hicks contractions do not get closer together, and unlike labor contractions, they tend to subside when you change position.