Many communities, chassidic ones in particular, have the custom to refrain from eating gebrokts on the first seven days of Passover. Gebrokts is a Yiddish word that refers to matzah that has come in contact with water. It literally means “broken,” and it has come to mean “wet matzah” because matzah is usually ground or broken up into crumbs before it is mixed with water.
Those who refrain from eating gebrokts on Passover do so for fear that during the baking process there may have been a minute amount of flour that did not get kneaded properly into the dough. Upon contact with water, that flour would become chametz.
The custom of not eating gebrokts gained prominence around the end of the eighteenth century. At that time, people began to bake matzahs much faster than halachically mandated, in order to be absolutely sure that the dough had no chance to rise before being baked. The flip side of this stringency is that the matzah we eat today is not as well kneaded as matzah used to be, and it is very possible that it contains pockets of flour.
The stringency of not eating gebrokts applies to matzah and water only—not to matzah and pure fruit juices or other liquids, which don’t cause flour to become chametz.
Those who are careful with gebrokts don’t eat matzah balls, matzah brei, or matzah anything; in short, they do not cook with matzah at all. Also, when there is matzah on the table, they are very careful to keep it covered and away from any food that may have water in it. Drinks, soups, and vegetables that have been washed and not thoroughly dried, are all kept far away from the matzah.
A situation in which this stringency comes into play is during the Korech step of the Seder. This step requires that we take maror—lettuce and horseradish—and put it between two pieces of matzah to make a sandwich. Because the lettuce will actually be touching the matzah, it must be absolutely dry. Many families spend much time carefully washing the lettuce and then very meticulously drying it in preparation for the Seder.
On the eighth day of Passover, which exists only outside the Land of Israel, the gebrokts stringency doesn’t apply, and all feast on matzah balls and matzah brei, and dip their matzah into soups and salads. In fact, many have the custom to try to eat their matzah with as many liquids and wet foods as possible.
The simple reason for this is that the celebration of the eighth day is of rabbinic origin.
But there is also a spiritual reason given for eating gebrokts on the eighth day:
The last day of Passover is connected with the future redemption (see Remembering the Future), a time when no evil will befall us. We reflect this reality by going out of our way to eat gebrokts on this day, without fear that the matzah may become chametz.
Alternatively, Passover celebrates the Exodus, a time when we were (and are) spiritually immature. At this time, we need to be constantly on guard for the slightest bit of chametz (i.e., pride and ego), lest we be adversely affected. Fifty days after Passover, and after the seven weeks of character refinement we undergo with the Omer counting, we have spiritually matured and are fully immunized against the harmful side effects of chametz. We are then ready as a nation to receive the Torah. Thus, on the holiday of Shavuot, one of the communal offerings brought in the Temple was specifically made of chametz. (For further elaboration on this idea, see Chametz: What Would Your Psychologist Say?)
On the last day of Passover, we have already completed the first of the seven weeks of the counting of the Omer. We are not quite ready for chametz, but we are a bit more secure. For this reason we eat our matzah with liquid, without fear.
For a lengthier treatment of the spiritual implications of gebrokts on the last day of Passover, see A Speck of Flour.