I think you may be referring to what are called "Braxton-Hicks" contractions.
Braxton Hicks contractions come from a Doctor named John Braxton Hicks. He was the first doctor to ever describe what these type of contractions were. This was back in the mid-late 1800s.
False Labor
There are multiple causes for Braxton Hick's Contractions. Typically, these contractions are caused by an extremely active baby or even dehydration. Make sure to contact one's doctor for more information or to schedule an appointment.
Labor contractions are painful and you can't ignore them. If they are not painful then they are just Braxton Hicks.
only in the last trimester when they prepare the uterus for labor and are called Braxton Hicks contractions.
Strengthens the uterus for the big day
It could be contractions or it could be false contractions (Braxton Hicks)
The strongest indication that contractions are occurring in association with true labor is that the contractions begin to occur at regular intervals. This is contrary to Braxton-Hicks contractions, which are spontaneous, random uterine contractions that do not occur with actual labor.
Braxton Hicks
Nope. Only some do. The lucky ones don't. The Braxton Hicks is just the preparation contractions. Letting you know that your baby is almost ready. They contractions come usually after 6 months. My doctor said there not supposed to hurt, but mines did. I thought I was in labor and I went to the doctor and my doctor sent me home saying that they are just Braxton Hicks and there nothing to be worried about.
Sometimes they can lead to some cervical change (including dilation, softening of the cervix, etc.). This is why it's important to call your care provider if you are having lots of Braxton Hicks contractions before you reach "full term" (or 37 weeks). On the other hand, even if your Braxton Hicks contractions are dilating your cervix, they might still be helping to rotate your baby into an optimal position for labor or even toning your uterus in preparation for labor. So even the contractions that aren't "real labor" are still doing something!