In the old days a phonebook was a list of names and numbers, like an asset database.
Now we have numbers on phones, with people search. Say I want to ring Gary at Safeness. I don't have a number for him but I know his company, and for others at that company I have the switchboard number. Wouldn't it be cool if people were linked to a company entity and we recorded the company numbers once for that entity so it could be found for everyone in that company?
Now we have the analogous equivalent of a CMDB (or a normalised database for the old farts amongst us).