HP codes
Hazardous properties HP1 to HP15
The short answer
The fifteen properties that make a waste hazardous, running from explosive and flammable through toxic and ecotoxic to HP15, a waste that can become hazardous after it has been disposed of.
In practice
They are what a hazardous entry in the List of Waste is asserting, and they go on the consignment note. A mirror entry is decided by whether any of them actually applies to the material in front of you.