A more thorough explanation:

Definition: A plea made by a woman who has been convicted of a serious crime, asking for her execution to be postponed until after she gives birth.

In the past, women who were sentenced to death or transportation (being sent to a penal colony) could plead their belly, which meant they claimed to be pregnant in order to avoid punishment. However, this plea was often met with suspicion, and a special jury of women (called matrons) would be appointed to examine the defendant and determine if she was truly pregnant or not.

If the woman was found to be "quick with child" (meaning she was far enough along in her pregnancy), her execution or transportation would be postponed until after she gave birth. However, if she was found to be lying about her pregnancy, she would still be punished.

Today, the plea of pregnancy is no longer used, but the law still prohibits the execution of pregnant women.

One famous example of the plea of pregnancy was made by Mary Surratt, who was convicted of conspiring to assassinate President Abraham Lincoln. She claimed to be pregnant in order to avoid being hanged, but the jury of matrons declared that she was not actually pregnant. She was executed anyway.