When you fly on a commercial flight, you might notice some bumpiness in the air as you go along your route. This is called turbulence, and it can range from very mild to severe. While it’s sometimes uncomfortable, it is very seldom deadly. The best thing to do is to keep your seat belt buckled, because that prevents you from getting thrown against the ceiling or walls in case the turbulence becomes severe. Turbulence is more frequent in late afternoon in summer when there are more thunderstorms around, but can happen any time of day or year and can even happen in clear air due to frictional effects from the jet stream, which is at the level that many jets fly at.
Travel and Leisure had an article on it recently which you might find interesting at https://www.travelandleisure.com/articles/what-is-turbulence?xid=NL_JustIn031316WhatExactlyIsTurbulence.
