It's just a term that has crept into the vernacular. Kind of like valve cover vs rocker cover, rear end vs differential or three on the tree vs three speed column shift. Some mistakenly refer to exhaust manifolds as headers. There are probably more.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine