Condensation trail: Since water is created in the process of burning fuel, it will condensate in the wake of the aircraft as ise if is sufficeintly cold. It will take some time for the ice to sublimate and a white trail can be seen.
chemtrail: Some popel believe that the white trail is made up not (only) from ice, but from dangerous chemicals.
Since chemicals are generally expensive it might be asked why anyone should distribute them into the atmosphere.
So that would be the point to debate.