On this topic, wikipedia says "After launching the architecture under the "x86-64" name, AMD renamed it AMD64 in 2003; Intel initially used the names IA-32e an

On this topic, wikipedia says "After launching the architecture under the "x86-64" name, AMD renamed it AMD64 in 2003; Intel initially used the names IA-32e and EM64T before finally settling on Intel 64 for their implementation. x86-64 is still used by many in the industry as a vendor-neutral term, while others, notably Sun Microsystems (now Oracle Corporation) and Microsoft, use x64."