A distrail is the clear path through a cloud formed in the wake of an aircraft.
Distrails form because the aircraft turns the water droplets in the cloud into gas or ice.
In some ways they can be thought of as a ‘negative contrail‘. (A contrail is where an aircraft wake creates a long thin cloud.)
They are not the same and should not be confused with ‘contrail shadows‘, where a contrail casts a shadow, forming a long thin dark line on a lower cloud.
You might also enjoy:
The Secret World of Weather – The Book