I call them finish 2x4s, lumber has always be sawen at full dimension 2"x4". The 2"x4"s then are dried then planed down to perfectly straight 1-1/2" x 3-1/2" x 8'.
Around here 50 years ago there was sawmills everywhere, stacks and stacks and stacks, BIG stacks of lumber everywhere, now very few sawmills across Maine, most logs now are taken up across the border to that other country, cant think of the name right now, but up there they saw up the logs and truck the lumber back to HD and Lowes..........So the the logs go north, then comes back in lumber and people like me buy these portable sawmills and we live happily ever after.......................................