Scavenging is the obtaining of information left around a computer system, in the computer room rubbish bins, etc. Bin diving (called 'Dumpster Diving' in the US) also involves obtaining sensitive information from an organisation's rubbish receptacles and bins.
This also refers to scavenging from areas of hard disks that are not in use by files but are currently 'file slack' or 'unallocated clusters'