is a specific kind of: fir, fir tree, true fir.

is a broader term that covers: Abies amabilis, amabilis fir, Christmas tree, Pacific silver fir, red silver fir, white fir | Abies alba, Christmas tree, European silver fir | Abies concolor, Abies lowiana, California white fir, Colorado fir, white fir | Abies balsamea, balm of Gilead, balsam fir, Canada balsam | Abies fraseri, Fraser fir | Abies grandis, giant fir, grand fir, lowland fir, lowland white fir | Abies lasiocarpa, Alpine fir, subalpine fir.