A gust is a strong, short burst of air. If you're walking around on a brisk, cold day, hold on to your papers tightly — a gust of wind could sweep in and send your notes flying into the air.
You've probably seen the famous image of Marilyn Monroe standing on a sidewalk with her white dress blowing in the breeze from a subway grate — that might be the most famous gust of air in popular culture. Gust comes from the Old Norse word gustr, meaning "a cold blast of wind." Gust also can be used to describe other things that come on with a sudden burst, like a violent gust of rain or an unexpected gust of sadness.