Short answers, pulled from the story.
A reconnaissance satellite gathers information for military or intelligence purposes, including photography, signals intelligence, and detection of missile launches or nuclear explosions. It differs from satellites built for science or public communication.
The United States Air Force ordered development of an advanced reconnaissance satellite on the 16th of March 1955, with the goal of providing continuous surveillance of an enemy's war-making capability.
CORONA satellites took photographs and ejected canisters of film, which descended by parachute and were retrieved in mid-air. The program ran from 1959 to 1972 and helped photograph denied areas and replace the U-2 spy plane.
Zenit was an unmanned Soviet reconnaissance satellite that flew from 1961 to 1994, with its final flight carrying only a test payload. It grew out of the same decree that authorized the Sputnik program and, along with Vostok, was one of two designs that emerged from it.
The main types are missile early warning, nuclear explosion detection, electronic reconnaissance, optical imaging surveillance, and radar imaging surveillance. Their earliest known examples were the Missile Defense Alarm System, Vela, SOLRAD, Corona, and the Soviet US-A series.
KH-11 reconnaissance satellite photographs were sent to Jane's Defence Weekly in 1984, and in 2019 President Donald Trump tweeted a classified image showing the aftermath of a failed test of Iran's Safir rocket.