Short answers, pulled from the story.
A flyby is a spaceflight operation in which a spacecraft passes near another body, usually the target of the mission, sometimes gaining a gravity assist toward another target in a swing-by. The most important parameters of any flyby are the time and distance of closest approach.
Apollo 13 suffered an exploded oxygen tank, and this forced the spacecraft to fly by the Moon rather than land on it as originally planned.
Cassini-Huygens, launched in 1997, achieved 126 flybys of Saturn's moon Titan, starting with its first flyby in October 2004 and ending with its final close flyby on the 22nd of April 2017.
New Horizons performed the most distant flyby to date of Arrokoth on the night of the 31st of December 2018 into the morning of the 1st of January 2019, at a distance of 43.6 astronomical units from the Sun.
The 1969 flyby's infrared radiometer results showed that Mars's atmosphere was composed mostly of carbon dioxide, and the instruments detected trace amounts of water on the surface.
International Cometary Explorer, formerly named ISEE-3, passed within 7800 kilometers of Comet Giacobini-Zinner's nucleus on the 11th of September 1985, flying through the comet's plasma tail.