What the programme is
Iran has declared civilian nuclear facilities for power generation and research, including enrichment sites at Natanz and Fordow, the Bushehr nuclear power plant, and the Arak heavy-water reactor. The programme operates under the Non-Proliferation Treaty and IAEA safeguards, with the depth of safeguards access varying by political agreement.
Enrichment, in plain English
Natural uranium contains less than 1% of the isotope U-235. Civilian power reactors typically use uranium enriched to 3–5% U-235. Research reactors and medical isotope production use up to 20%. A nuclear weapon requires roughly 90% U-235 ("weapons grade"). The difficulty of enrichment is non-linear: the last leg from 60% to 90% requires much less work than the first leg from natural to 5%.
"Breakout time"
Breakout time is the estimated number of days or weeks an enrichment programme would need to convert its existing stockpile to enough weapons-grade material for one device, if a political decision to do so were made. It is a function of stockpile size, enrichment level, and centrifuge capacity. It does not factor in weaponisation (engineering a working device from the material), which is a separate, longer process.
The IAEA reports
The IAEA Director General's quarterly reports on Iran are the most authoritative non-aligned data source on the programme. They cover enrichment levels, stockpile sizes by enrichment level, inspection access, and any outstanding safeguards questions. They are technical documents, publicly available, and routinely characterised differently by different parties to the dispute.