It used to be when I went to the lumber store the inexpensive soft wood was Pine. Now they call it "White Wood", what exactly is "White Wood", I don't recall ever hearing of a tree species by that name.
I suspect it is any cheap tree that is fairly white. 'White wood' is not a species. It is likely pine, but in theory could be balsam or aspen or a bunch of others.
I did a little looking and it mostly confirmed that. It can be any of a number of species that all are fairly 'white' with little strong grain showing.
White wood is the cheap, crappy wood available at home centers, and will vary by region. Here in Arizona, it's white pine.
That's a deliberate misuse of the poor tulip tree's name. White wood is Liriodendron tulipifera, a rather valuable hardwood (which funnily is not white at all).
Insofar, calling the inexepensive soft wood "white wood" is somewhat misleading.
Nevertheless, in practice, home improvement centers will sell anything from spruce, fir, or pine to "coniferous wood" under the umbrella term "white wood". In other words, you get whatever happens to be around and is cheapest, but it sounds like you buy something valuable.
In Canada anyways, you would also see it referred to as SPF - Spruce, Pine, Fir which is used as dimensional framing lumber.
The meaning of "white wood" or "whitewood" may vary by region.
In the UK, for example, it usually means timber primarily intended for "first-fix" use where it will not be visible when the work is completed.
The species probably depends on what is available in the region but can include Spruce, Douglas Fir, Pine and so on. Spruce seems to be most common in the UK.
There is a fast growing pine species called radiata pine that is grown in New Zealand that Home Depot sells. They sometimes mislabel it white pine but it not eastern white pine. Now they call it white wood.