In food service what is the difference between a purchase order and a specification?

A purchase order is a document asking you to supply a particular product or products. It always states the quantity and price, delivery address, invoice address, but depending on the kind of product it may also state the colour, size, quality, delivery time, or any other particular characteristic the product or products should have.

A specification is a document detailing the exact nature of a product. It may be provided by the supplier to tell the purchaser exactly what they will get, or it could be used by the purchaser as an enquiry, e.g. "can you provide 1000 nails with the following specification ... Mild steel, zinc plated, 3 inches long, flat head".

Realise that when/if he orders the purchaser will usually repeat the specification as part of the purchase order just as my first paragraph shows.

So Purchase Orders usually contain a repeat of the Specification