"solo flight time" means, with respect to the flight time necessary to acquire a permit, licence or rating,
(amended 2003/06/01; no previous version)
(a) in the case of a pilot, the flight time during which the pilot is the sole flight crew member, and
(b) in the case of a student pilot permit holder, the flight time during which the holder is the sole occupant of an aircraft while under the direction and supervision of the holder of an instructor rating for the appropriate category of aircraft; (temps de vol en solo)
In the case of the student pilot, it is indeed very clear and the definition is as expected.
The surprise comes with definition (a). It seems to suggest that if the applicant who is already a licence or permit holder, then there there can be more than one occupant on board the aircraft and the pilot can still log it as "solo." I am curious to know whether Transport Canada interprets the presence of a person who has an Instructor Rating on board the aircraft which is type certificated for one pilot, and who is simply "riding along" as a passenger and not acting in the capacity of an instructor, complies with definition (a)?