That begs a good question - what is Traveller? The rules mechanism or the setting? I'd say the rules because we all have some sort of IMTU but at the core we all use hexidecimal chargen stats of some sort.
Note that there was backlash in 1987 - when GDW released 2300 as Traveller 2300, and it was similar in scope, but mechanically and setting-wise different.
There was backlash again when TNE "reset" the setting with Virus and didn't use a d6's only mechanic.
And there was backlash in 2008 when Mongoose's Matthew claimed that there "is no Official Traveller Universe"... The number of ATUs seeing commercial success at the moment appears to be 2: 2300 - which is a port of a not-quite Traveller-but-Traveller-Branded ruleset to MGT, and is the second such port (the other being for T20).
Only a handful of grogs are really insistent it's the ruleset - and they generally ignore all non-Classic rulesets.
And only a handful of newbs are doing so, either - but for them, it's MGT.
And only 3 editions are setting-less ... CT 1E, and MGT 1E & 2E. Even then, it's not generic in the same sense that GURPS or Savege Worlds is. Lots of setting implied in the mechanics of CT 1E & both MGT editions. Some of it inconsistent.
But, judging by Don's hermeneutic, and Marc's usages, Traveller is, fundamentally the setting's timeline.