1. An occurrence, especially one that is particularly significant, interesting, exciting, or unusual: When the town finally had its 800th anniversary of existence , everybody wanted to take part in preparing the festivities for the memorable event.

Events can also be significant milestones, consequences, or happenings in the present, past, or the future.
2. A thing that happens or might happen at a given place at a given time: In the event that Mrs. Smith is late, a substitute teacher will take her place in the classroom.
3. An organized occasion: An event can be a social function or sports competition.
4. Any of the races or other competitions that form part of a larger sports occasion: One of the biggest events for people all over the world are the Olympic Games.

A large increase of electric and radio wave density in the D-level of the atmosphere caused by electron-bombardment of the atmosphere during an aurora or a geomagnetic storm.

A classification for a weather event that is very different from the "normal" range of weather that is experienced in a given geographical location: Some examples of extreme weather events include a flood, a drought, a tornado, a blizzard, an ice storm, a heat wave, a cold spell, etc.

1. Any event in which ionization occurs, commonly caused when an electron or a photon with sufficient energy passes through a sample of matter.
2. Any occurrence in which an ion or group of ions is produced; for example, by passage of charged particles through matter or the passage of alpha or beta particles or gamma rays through a gas.