An eruv is a ritual zone typically marked by wire or string that makes certain activities otherwise forbidden on the Sabbath possible for Orthodox Jews. There are numerous restrictions on activities on the Sabbath, which runs from sundown Friday to sundown Saturday, related to a prohibition on working on what's supposed to be a day of rest. For example, carrying keys, money or even babies — even pushing children in a stroller — is prohibited. But an eruv expands the private walls of the home, relaxing those restrictions.