An oid is an Object IDentifier, an integer identifying a first-class object such as a dob or pob within the MetaVerse.
oids are assigned sequentially; at the time of writing, most oids are in the 9-digit range with values reaching up into the high 300 millions. Very old objects and avatars have 8-digit oids.
An oid that identifies a dob is referred to as a doid; one identifying a pob is referred to as a poid.
See also: TechnicalOverview.