The Gemara in Masechet Pesachim (101) records the Halacha taught by Shemuel, "Ein Kiddush Ela Be'makom Se'uda." This means that one fulfills the obligation of Kiddush only if he recites or hears Kiddush in the place where he will then eat a meal. If one recited or heard Kiddush in one place, and then left without eating a meal, he has not fulfilled his obligation of Kiddush and must recite or hear it again.
This Halacha gives rise to the question of how we define a "place" in this regard. Does a person fulfill his obligation if he moves to a different table after Kiddush to eat his meal? Occasionally at large Shabbatons and the like all the participants in the function gather around one table to hear Kiddush, and then they all return to their individual tables for the remainder of the meal. Does one fulfill his obligation of Kiddush if he eats at a different table from the one where he heard Kiddush?
According to Halacha, one satisfies the requirement of reciting Kiddush in the place where he eats if he eats in the same room where he hears Kiddush. Even in a very large ballroom, if one moves from one corner of the room to the other after Kiddush to eat his meal, he has fulfilled his obligation. Nevertheless, it is preferable for one to eat his meal in the place where he recites or hears Kiddush; moving from one area in the room to another is acceptable only Be'di'avad after the fact, or if there is no alternative.
If one moves to a different room after hearing Kiddush to eat his meal, he fulfills his obligation only if his new location is visible from the initial location. If a person standing in each location can see the other, then we consider the two locations one "place" with regard to this Halacha, and therefore one indeed fulfills his obligation in such a case. Of course, this leniency, too, works only Be'di'avad; ideally, one should endeavor to hear Kiddush in the same place where he will eat his meal. And if one moves after Kiddush to a different room which is not visible from his original location, then he must recite or hear Kiddush again before eating.
How do we define a "meal" for purposes of this Halacha? How much must one eat after Kiddush for the Kiddush to be considered to have taken place in the place of one's meal?
A "meal" in this respect is defined as a minimum of a Kezayit of Mezonot (grain products), or a Revi'it of wine or grape juice. After hearing or reciting Kiddush, one must eat at least a Kezayit of Mezonot food or drink a Revi'it of wine or grape juice followed, of course, by the appropriate Beracha Acharona in order to fulfill the requirement of Kiddush.
Unfortunately, many people are unaware of this Halacha and, after hearing the Kiddush recitation in the synagogue on Shabbat, take just a sip of wine or eat a small cookie and assume that they have fulfilled their obligation. If one does not eat at least a Kezayit of grain products or a Revi'it of wine or grape juice, he has not fulfilled his obligation of Kiddush. One must therefore ensure after hearing Kiddush on Shabbat to partake of at least these amounts of either Mezonot or wine or grape juice.
Summary: In order to fulfill the obligation of Kiddush on Shabbat, one must recite or hear Kiddush in a place where he will then eat a meal. A "meal" for purposes of this Halacha refers to a minimum of a Kezayit of grain products, or a Revi'it of wine or grape juice. If one moves to a different place in the same room after hearing Kiddush, and he eats his meal in the new location, he has nevertheless fulfilled his obligation, even in a large ballroom. The same applies if he moves to a different room but his original location is visible from his new location. Preferably, however, one should ensure to recite Kiddush in the same place where he will eat his meal.
