“Chemtrails” is what conspiracy theorists call “contrails”.
Contrails is a portmanteau of “condensation trail”. They don’t under stand physics and believe that the airlines and everyone else are literally spraying chemicals into the air for some nefarious (usually govermental) purpose (usually to mind control people)
They’re stupid.
For people wondering, contrail is caused by moisture in the jet engine exhaust cooling and becoming a cloud,