Carrying objects between public and private domains is forbidden on Shabbos, as is carrying items within a public domain. An עירוב is a mechanism outlined in Halacha that changes the classification of a public domain to a private one. The word עירוב, in the vernacular, has come to mean the enclosure of a specific area for the purpose of permitting carrying on Shabbos. Technically the form of enclosure used in most instances is a צורת הפתח (literally "the form of a doorway"). This צורת הפתח generally consists of upright poles which are the sideposts and wires running from them which form the lintel. In addition to the Tzuras Hapesach, which renders the entire area a רשות היחיד (private domain), there must also be an עירוב חצירות (lit. combining of courtyards), through joint ownership of bread, usually matzos. If it also encloses non-Jewish residents שכירות רשות (renting of rights) must also be performed. The details of these processes are beyond the scope of this flyer.
An עירוב is meant to enhance the enjoyment and honour of Shabbos by permitting us to carry within its borders. Besides saving those who do carry on Shabbos from this עבירה, an עירוב allows those who are homebound - the infirm and parents caring for infants - to go to shul and to visit friends and family on Shabbos, as well as the carrying of other permitted items necessary for Shabbos. Items required for use after Shabbos may not be carried on Shabbos. Any item that is מוקצה, including an umbrella even if opened before Shabbos, may not be carried on Shabbos. At the same time, it continues to be the responsibility of parents to teach their children the הלכות and restrictions of carrying on Shabbos. It is only because of the עירוב that we are allowed to carry within the area it encloses. Everyone, including children, should be aware of the proper Halachic behaviour in areas where there is no עירוב.