Breakout time, monitoring and verification, military dimension, stockpiles - all the jargon explained
The point of an agreement is to increase Iran's nuclear "breakout time", the time needed to produce enough highly enriched uranium or bomb-grade plutonium for a single weapon, to at least a year from the current two to three months.
The United States missed a 0400 GMT Friday congressional deadline to submit the text of a final agreement and have a 30-day review during which President Barack Obama will not be permitted to suspend congressional sanctions through executive order.
If a deal is transmitted to Congress by Sept. 7, a period that includes the congressional August recess, US lawmakers will have up to 60 days to review it.
US officials had previously expressed concern that the extended review would provide more time for any deal to unravel but, in the last week, they have said an extension did not matter.
If a deal were sent to Congress after Sept. 7, the review period reverts to 30 days.
US, EU and UN sanctions will be suspended and later terminated, based on verification of Iran's compliance with the agreement.
UN nuclear-related sanctions will need to be removed on the basis of a Security Council resolution, which will also allow Iran to purchase specific nuclear technology that it has been banned for years from acquiring. There would be a "snapback" plan to restore the sanctions in 65 days if Iran violates the deal.
The six powers also wanted the resolution to simultaneously reimpose a UN arms embargo on Iran and ballistic missile sanctions, which they described as not nuclear-related. This was one of the main sticking points in the final phase of the talks. Iran insisted the ban on conventional weapons and ballistic missiles was nuclear-related and should also be lifted. Russia, which sells Iran weapons, spoke in favor of Iran's position.
Iranian negotiators agreed in Lausanne that Tehran's uranium enrichment program will be subject to limitations for a period of 15 years, easing gradually after 10.
Machines that purify uranium for use in nuclear power plants or weapons. In Lausanne, Iran agreed to reduce its roughly 19,000 centrifuges installed at two enrichment facilities, Natanz and Fordow, to 6,104. Under the deal, only 5,060 of these, those at Natanz, will be active for the first 10 years.
All 6,104 centrifuges are to be first generation IR-1s. Iran also agreed to not enrich uranium beyond 3.67 percent of fissile material for at least 15 years, well below the 90 percent or more needed for weapons, but appropriate for civilian use. Iran would be prevented from installing further centrifuges for 15 years.
RESEARCH AND DEVELOPMENT
This was one of the more difficult sticking points. According to a French fact sheet, Tehran would be allowed a "gradual and precisely defined increase in (enrichment) capacity between the 10th and 13th years, with the introduction of advanced IR-2 and IR-4 centrifuges".
MONITORING AND VERIFICATION
One of the biggest sticking points in the talks was monitoring and verification of the deal's implementation. The most contentious issues were access for International Atomic Energy Agency inspectors to Iranian military sites and nuclear scientists. Iran's Supreme Leader Ayatollah Ali Khamenei has said military sites and scientists are off limits. Iranian and Western officials said so-called "managed access", or access that is limited to protect legitimate military secrets, such as by blindfolding the inspectors when they are taken to a site, would be possible.
Iran is to reduce its current stockpile of about 8,700 kg of low-enriched uranium (LEU) to 300 kg of 3.67 percent LEU for 15 years. Iran has been reluctant to ship its LEU abroad, and wants to convert much of it to a less proliferation-risky form. This has been a sticking point.
ARAK HEAVY-WATER REACTOR
Iran agreed to redesign and rebuild the Arak heavy-water research reactor based on a design agreed by the six. The idea is that it will not produce bomb-grade plutonium and will focus on peaceful research and medical isotope production.
POSSIBLE MILITARY DIMENSIONS ("PMD")
According to the Lausanne agreement, Iran must answer queries the IAEA has about past activities that may have been related to atomic weapons research. But Iran has been stonewalling the IAEA probe, and Western officials have said some of the sanctions relief would depend on Iran resolving those queries.
Officials close to the talks said they have made progress on this issue, while the IAEA has said it could issue an assessment of its investigation by the end of the year if Iran cooperates.
Israel and Saudi Arabia, Iran's regional foes, are suspicious of Iran and oppose the deal. Iran has become increasingly assertive in the region and some analysts believe that, if Iran secures sanctions relief based on a deal with the West, it will boost its confidence as a regional power and improve its flagging economy.