Once, we competed for kudos with the labels on our clothes. Today, it is the labels on our food that matter.

As large segments of society have decided that organic is a must-have, in kosher-observant circles, prestigious rabbinical certifications have become increasingly important.

Take a trip to a kosher supermarket anywhere in the world and you will see shelves loaded with goods boasting all sorts of kashrut credentials, such as glatt, mehadrin and yashan.

"Once upon a time people commonly thought ‘either its kosher or it is not,'" says Rabbi Jeremy Conway, director of the London Beth Din Kashrut Division. "But today they readily understand that just as there are differing standards of cuisine, design and healthcare, so there are different standards of kashrut."

If you are confused by the words on the labels, don't worry. It seems that many of the certification connoisseurs - and the rabbis who write the labels - are, too.

You can buy dozens of "glatt" products these days, including chickens and fish balls - even though glatt is a term that can only apply to beef.

Here is a glossary of the terms for next time you are shopping:

Glatt
Glatt is a Yiddish term which means smooth. In kashrut, it refers to the lungs of a slaughtered cow.
Several important rabbinic authorities say that a cow is kosher if there are growths on the lung, so long as they are removed. But others are stricter, claiming that a cow should not be eaten unless the lung is smooth, or glatt.

Different authorities give different standards of just how smooth the lung must be. The strictest is what is known as Glatt Beit Yosef. This means it is glatt in line with the definition of Rabbi Joseph Karo (known as the Beit Yosef) who wrote the Shulchan Aruch legal code.

There is no such thing as glatt lamb. It cannot apply to chicken either.

Yashan
Yashan is Hebrew for old and usually refers to baked goods. But it does not mean that the bread bearing this label is stale.

The Torah forbids eating a season's grain - wheat, oats, barley, spelt and rye - until the grain offering had been taken to the Temple by way of thanks to God for the harvest. This happened on the second day of Passover.

This meant that until the offering was made, the season's grain was deemed "new" and off-limits. Once Passover passed, it became "old" or yashan, and permitted.

When Jews moved to the diaspora in the centuries after the destruction of the Temple, many religious authorities ruled that this regulation only applied in the Land of Israel. After all, grain offerings were no longer taken to the Temple and the seasons were different in the lands where they were now living.

However, some stricter authorities said that people should continue to observe the rule. This approach has become increasingly popular across the diaspora in the last decade, including in Britain where two kashrut authorities - Kedassia and the Federation of Synagogues - have begun to promote it.

Mehadrin
Mehadrin means beautified, and is a blanket term for any religious precept observed to a particularly high standard. Many products boast this benchmark, and it is difficult to know exactly what they mean. "It can be a very subjective term," admits a top supervisor at a British kashrut authority. "What we call mehadrin others simply call ‘kosher'. But what others call mehadrin we may call ‘only just kosher'."

In reality, supervisors can use the term whenever it suits them and there is no way of knowing exactly what it means. "People ask me why I don't put mehadrin on everything," says Dayan Moshe Elzas, head of kashrut at the Federation of Synagogues. He says that there would be little to stop him - he just avoids doing so because he wants to avoid devaluing the term.