The Labour Party's ruling body, the National Executive Committee, has agreed to adopt the International Holocaust Remembrance Alliance's definition of anti-Semitism in full, with all of its examples.
The definition was designed to provide a common definition for use by law enforcement across Europe.
In England and Wales, it's just one of a range of guidelines used by police forces (as well as other public bodies) to help them decide whether to treat an incident as anti-Semitic. Those tools include anti-racism legislation.
Anti-Semitism has been on the rise in the UK, according to incidents recorded by charity the Community Security Trust (CST), which works with the community and with police forces.
The CST recorded 727 anti-Semitic incidents across the UK in the first six months of 2018 - the second highest figure recorded in more than two decades.
The highest-ever number was recorded in the first six months of last year (786).
In the whole of 2017 there were 1,414 incidents, compared with 541 in 2008. At the time, this was the third-highest annual figure that had been recorded since the CST began in 1984.
The charity defines anti-Semitism as "any malicious act aimed at Jewish people, organisations or property, where there is evidence that the victim was targeted because they are, or are believed to be, Jewish".
Most of these will be crimes but some incidents don't meet that threshold.
Three-quarters of the incidents recorded in the first half of 2018 fell into the category of "abusive behaviour". That includes anti-Semitic graffiti, one-off hate mail, verbal abuse and abuse on social media.
Incidents of this type have more than tripled since 2008.
The numbers of reported threats made verbally, face-to-face or on social media have also more than tripled in the past 10 years, from 16 to 53. Three of these in the first six months of 2018 involved victims being threatened with a knife.
The more serious incidents including assault and extreme violence are less common. But numbers of assaults have been higher than usual in the past couple of years: 80 in the first half of 2017 and 59 in the first half of 2018.
Assault numbers were below 45 in every other year but one out of the previous 10.
Damage and desecration of property and grave sites and the distribution of anti-Semitic literature have also risen but by smaller amounts.
Faith- and race-based hate crimes are recorded on a national level, but they are not broken down by individual religion.
Across England and Wales, there were 5,949 hate crimes recorded by the police where the victim's religion was a factor in 2016-17. This has almost quadrupled since 2011-12, outstripping the overall rise in hate crimes.
The Metropolitan Police does provide this breakdown for London, where there were 514 anti-Semitic incidents in the 12 months to July 2018.
In the 12 months to March 2011, when the Met Police data began, there were 194 incidents.
Meanwhile, in Scotland there's been a slight fall in the numbers of religiously aggravated charges.
There were 678 charges reported to the procurator fiscal - the Scottish public prosecutor - in 2016-17, down from 896 five years earlier. That was a particularly bad year though - it was 694 the year before that.
The UK is a member country of the International Holocaust Remembrance Alliance (IHRA) and has adopted its definition of anti-Semitism on a national level.
The NEC's decision to include all examples of anti-Semitism set out by the IHRA in its code of conduct means they could be used to discipline members.
Writing in the Evening Standard newspaper, Jeremy Corbyn said the number of cases of anti-Semitism over the past three years represented less than 0.1% of Labour's membership.
BBC Reality Check understands this amounts to approximately 300 cases since 2015.
The Labour Party did not provide any details of the outcomes of these cases.