The adjective kasher or kosher means ‘fit for purpose according to Jewish law’. The noun from kosher is kashrut, which usually refers to the Jewish dietary laws, but these terms are also used in other contexts too, such as about religious artefacts. For example, a Torah scroll or mezuzah with even one damaged letter would not be kosher.

The main rules of kashrut are:

Animals are only kosher to eat if they have the characteristics listed in the Torah – cloven hooves and chew the cud – so for example beef and lamb, but not pork, horse, or camels.

Bird species that are kosher are listed in the Torah but it is difficult to identify them in modern terms, so only those recognised by tradition are eaten. Generally birds of prey are not kosher, and domestic fowl such as chicken, duck, and turkey are kosher.

Fish are only kosher to eat if they have fins and scales, so for example salmon, haddock, and herring, but not eels.

Shellfish and insects are never kosher.

Milk, eggs, and other animal products are only kosher if they come from a kosher animal.

The laws of kashrut teach compassion, and concern for animal welfare. These include shechitah – using an extremely sharp knife to kill an animal as quickly as possible in order not to cause it pain. People who carry out shechitah have to undergo a lot of training and follow very strict regulations.

Kosher butchers, bakers, and restaurants have prominently displayed certificates confirming that their businesses follow all the laws of kashrut, and many ordinary commercial food products have symbols on their packaging to indicate that the manufacturing process has been inspected and found to comply with kosher standards.

Some food products do not have a symbol on their packaging, but are listed in special guidebooks, apps, and websites, so that Jewish people can check which products are kosher. One example is the kosher search app provided by the kashrut department of the London Bet Din (Rabbinical Court).