Vapour trail, also known as contrail, is a visible trail of condensed water droplets or ice crystals formed by aircraft engines in the atmosphere during flight. However, there are several synonyms for the word vapour trail that are often used in different contexts. Some of the common synonyms include cloud trail, plume, streamer, jet trail, exhaust trail, and condensation trail. Depending on the cultural and geographical context, people also use different words to refer to vapour trail. For example, in America, they commonly use the term chemtrail to describe the vapour trail left by airplanes, which is a controversial term used by conspiracy theorists to describe a supposed chemical aerosol sprayed by the government for unknown purposes.