The story
From being a 64-bit architecture developed by AMD.
Etymology from Wiktionary, CC BY-SA 4.0.
AMD64
Today it means: The 64-bit version of the x86 instruction set architecture (as opposed to the original 16-bit x86 architecture, or to the 32-bit version of the x86 architecture, also known as IA-32, i386, or x86-32). Full definition →