Sounds like Braxton-Hick's - here's a link, plus the info:
http://www.allaboutmoms.com/bh.htm
" Braxton-Hicks Contractions
Episodes of tightening (contraction) of the uterine muscles are called Braxton-Hicks contractions. Although Braxton-Hicks contractions happen from very early in pregnancy, most women do not really notice them until the second half of pregnancy. Braxton-Hicks contractions are thought to play a part in toning the uterine muscle and promoting the flow of blood to the placenta. Some people call them practice contractions.
Braxton-Hicks contractions tend to be started off by either you or the baby moving, or by somebody touching your abdomen. Each Braxton-Hicks contraction may last 1-2 minutes. During this time, the whole uterus becomes hard. This may feel strange and rather uncomfortable. Braxton-Hicks contractions will not do three things and that is get longer in duration, closer together and last for a longer time period. Real labor will have contractions that are progressive and unable to be halted. Braxton-Hicks contractions may come and go. They may persist for hours on end and then cease to exist at all. Braxton Hicks contractions are not productive enough to promote the birth of the your baby. Braxton Hicks contractions usually are irregular in pattern and go away if you change your activity or drink water.
Braxton Hicks contractions can truly be as painful as real labor and make it even harder to distinguish the difference between the two. Again, the approach of determining if they are getting longer, stronger or closer together is the key. Real labor will persist and will not be persuaded to go away. However, if you are in doubt, contact your health care provider. "
Another one, if you want to check it out:
http://www.babycenter.com/refcap/pregnancy/childbirth/156.html
HTH! It's kind of weird to feel it happening and see your belly all tight, but I try to think of it as ab work without the effort!
Gotta get those muscles ready for the big day!