BitBLT
The operation that copies a rectangular block of pixels from one place to another and combines it with whatever is already there — the foundation stone of every window system before the 3D card.
Dan Ingalls wrote BitBLT, bit block transfer, at Xerox PARC in 1975 for Smalltalk on the Alto, and moved it into the machine's microcode once it turned out to be the only thing that mattered for performance. The call takes a source rectangle, a destination and a rule for combining the bits — copy, OR, AND or XOR — with an optional mask and a halftone pattern. It sounds trivial, but everything in an early window system is exactly that: text is drawn by copying glyph bitmaps out of a font image, a window scrolls by moving its own contents, a window is raised by copying it over the others, and the mouse cursor is drawn with XOR so that a second, identical operation erases it.
The name went everywhere. Bell Labs' Blit terminal was named after it, the Amiga's Blitter was a chip that did nothing else, X11 has it as XCopyArea with the function in its graphics context, the Macintosh as CopyBits in QuickDraw, and Windows still has BitBlt() in GDI with its 256 ternary raster operations. When graphics cards first accelerated anything, this was it, and when they stopped caring, because everything became textures on triangles, it became the first graphics primitive in history to retire.