This was unclear to me as well. “This holiday” is not a phrase I’ve ever really heard in casual conversation or in the media register. I know the British “go on holiday” but that means vacation.
Their PR/marketing department dropped the ball on this specific phrase. At the same time it seems that marketing department slip ups are common these days.
If they mean Christmas time, I.e. December or winter, they should just say December or winter. That would be more clear.
This is a particularly awful example of Americentrism. Going by season names is bad enough (this is a habit of Americans, Canadians and Europeans, which doesn’t work much beyond the northern hemisphere’s temperate and sub-arctic regions), especially for “fall”; but people in the rest of the world will normally eventually be able to figure it out. But this use of “holiday” is utterly unknown to most of the world and is nigh impossible to figure out without someone telling you what it is. As an Australian, I only learned about it last year, and my considered guess as to what it meant was wrong—I guessed somewhere in the middle of the year, when school is not operating during the summer. (We call the breaks between terms “school holidays”, most significantly of the summer break, which for us is mid–late December until the end of January or so.)
Which holiday? Christmas, Thanksgiving, New Year, Labor Day... Fourth of July?
Maybe Halloween would be appropriate, given how scary any major Windows upgrade is to enterprise orgs.
If they said "this holiday season", that would probably mean December timeframe, but they don't say that.
They repeat this confusing reference later on:
> The free upgrade will begin to roll out to eligible Windows 10 PCs this holiday and [...]