Gershon is correct that the most basic determiner of a thru-hike is that it gets done within one calendar year. For a very long time it was only applied to a hike that completed one of the Big Three long trails: AT, PCT or CDT.

None of this would matter one whit if there weren't a certain amount of prestige or status attached to the term "thru-hike". All the squabbling over defining who is a 'true' thru-hiker vs. who 'cheated' is really a fight over who gets to be in the clubhouse and wear the secret decoder ring.

I say it's all hiking and if it isn't rewarding enough for its own sake then you probably should change how you are doing it.