The leaders of North and South Korea declared at a summit Friday they had a "common goal of realising, through complete denuclearisation, a nuclear-free Korean Peninsula".
Exactly what that means remains unclear ahead of a much-anticipated summit between North Korean leader Kim Jong Un and US President Donald Trump.
The White House has urged "the denuclearisation of North Korea", but the distinction is crucial -- that is an explicit reference to only one country, while the broader term is open to interpretation on both sides.
The North -- which invaded its neighbour in 1950 -- is the only one of the two Koreas to possess nuclear weapons, but the South has a security alliance with the most powerful nation on the planet.
What weapons does North Korea have?
Estimates of Pyongyang's arsenal vary.
Monitoring groups put the size of Pyongyang's sixth and last atomic blast in September at 250 kilotons -- 16 times the size of the US bomb that destroyed Hiroshima in 1945 and the kind of yield generated by a hydrogen bomb.
Seoul's 2016 defence white paper -- the most recent available -- estimated the North had 50 kilograms of plutonium -- reportedly enough for about 10 bombs - and a "considerable" but unquantified ability to produce uranium weapons.
Last year, the Washington Post reported a US intelligence assessment that the North had up to 60 nuclear devices.
Where the North keeps its missiles is not publicly known, but it has extensive experience in tunnelling and it is believed they are stored at underground facilities scattered around the country.
They are also mobile -- it has put transporters on show at military parades.
What does the US have?
US President Donald Trump says his nuclear button is bigger than Kim's -- and it works.
According to the State Department, as of September 1, the US has a total of 1,393 deployed nuclear warheads, deliverable by land- and submarine-based missiles and heavy bombers.
It has thousands more in stockpiles and awaiting dismantlement, campaign groups say, with the Arms Control Association putting the total at 6,550 last year.
The US withdrew tactical nuclear weapons from the South in the 1990s and Seoul does not have any itself.
But the US has an unparallelled ability to project power around the world and can reach targets anywhere with conventional or nuclear munitions.
It has long-range bombers, mid-air refuelling capabilities, and a fleet of nuclear submarines constantly at sea, each armed with phenomenal destructive power.
What has Pyongyang promised?
According to Trump "they have agreed to denuclearisation". Asked what he meant by the term, he told reporters earlier this month: "It means they get rid of their nukes -- very simple."
But North Korea itself has made no explicit pledge to do so during the current rapprochement.
According to Seoul, it has offered to consider giving them up in exchange for unspecified security guarantees.
When Kim visited key backer China last month in only his first foreign trip as leader, China's state media cited him saying that the issue could be resolved if Seoul and Washington take "progressive and synchronous measures for the realisation of peace" -- implying some form of quid pro quo.
What does that imply?
Pyongyang says it needs nuclear weapons to defend itself against the United States, and interprets threats against it widely -- it has regularly condemned US-South Korean joint military exercises as preparations for invasion.
Under the 1953 Mutual Defence Treaty between South Korea and the US, Washington is duty-bound to come to its ally's aid if attacked.
In the past Pyongyang has demanded the end of the alliance and the withdrawal of US troops from the South.
The US has 28,500 troops stationed in the country to defend it from its neighbour, and Washington's nuclear arsenal is a key part of its defence capabilities -- it does not have a "no first use" policy.
What has the North promised before?
Friday's declaration was the first time the word "denuclearisation" has appeared in an inter-Korean summit communique.
There was no reference to the subject in the declaration after their first summit in Pyongyang in 2000, and seven years later they said they would work together to implement two existing agreements on "the nuclear issue on the Korean Peninsula".
But one of those documents, the Joint Statement of the Fourth Round of the Six-Party Talks issued in Beijing in September 2005, is unequivocal.
"The DPRK committed to abandoning all nuclear weapons and existing nuclear programmes," it said, using the North's official name.
But it carried out its first nuclear test the very next year. Another agreement followed before Pyongyang walked out of the six-party process -- which brought together the two Koreas, China, the US, Russia and Japan -- in 2009, detonating its second atomic blast months later.