People and institutions
ExComm: the Executive Committee of the US National Security Council, formally established on 22 October. Kennedy and his advisers had already been meeting since 16 October.
OAS: the Organization of American States, the regional body whose support Washington sought for the quarantine. UN: the United Nations, where U Thant pursued mediation and Adlai Stevenson presented the American case.
Sources for this passage: [1] [2] [3]Operations and intelligence
Quarantine: the American term for the selective interception of prohibited military deliveries to Cuba. It was enforced at sea and backed by the possibility of further force.
Reconnaissance: gathering information through observation, including photographs taken from aircraft. Interpretation adds judgements about what the images show; those judgements may be revised as evidence develops.
Sources for this passage: [4] [5]Missiles, warheads and readiness
A missile is a delivery vehicle; a warhead is its destructive payload. Finding a missile does not by itself establish where its nuclear warhead is or whether the system is ready to launch.
Strategic weapons are generally intended to affect the wider course of a war, including attacks on an opponent's homeland. Tactical nuclear weapons are associated with battlefield or local military use. Tactical does not mean harmless: their use could kill on a large scale and trigger wider escalation.
DEFCON means defence readiness condition in the American military system. Statements about DEFCON should identify the command concerned. SAM means surface-to-air missile, a weapon directed against aircraft.
Sources for this passage: [5] [6] [7]