What is an Eruv

An eruv is a collaboration שיתוף of the people in a courtyard or a city with all contributing a type of food commonly flour to create bread (matza)זיכוי הפת, or taking Matzos and having it represent the entire community. The Rabbi represents the people in unity to symbolize we are united as one in one domain. the Rabbi or representative then makes the blessing saying through this partnership and collaboration it would be permissible for the inhabitants residing in this courtyard or this city to carry food or other necessities for Shabbos.
A requirement of the eruv to make an היקף symbolic boundary by erecting virtual doorways צורת הפתח or fences מחיצות in the perimeter of the enclosure that is included in boundaries of the eruv.

זיכוי הפת של העירוב