From the people who wrote the ISO 9000 series:
"Policy" used to be defined in ISO/TC 176/SC 2/N 526R. They have removed it from the latest version of that document (ISO/TC 176/SC 2/N 526R2).
"Procedure" is defined in ISO 9000:2005 (and I recall seeing it posted on the Cove).
"Work Instructions" (sic
) is defined in ISO 10013:2001.
Of course, anybody can define anything any way they want. If you don't believe me, go check this link: