Artifact originating from P5C-353. When the inhabitants of this world discovered their planet was going to be destroyed of all life they constructed the Orb, the embodiment of their civilization, composed of countless intelligent entities at the microscopic level.
On the surface, the Orb is covered entirely of alien language, with the equivalent of a thousand pages of text. Daniel Jackson deduced a "sort" of Page One, but his theories were laid aside when the Orb reared its true purpose.
The entities within the Orb had an incredible urge to multiply and spread. They hoped that, one day, travelers would come and remove the artifact to a world rich in oxygen and to consume.
Having discovered Earth, the occupants of the Orb were threatened when they realized Jack O'Neill and Teal'c were attempting to return it to 353. In an act of desperation it planted itself into the concrete cement of the Gate room, as well as inhabiting Jack O'Neill by directly interfacing with him, piercing his shoulder trapping him against the concrete.
Once the base personnel realized the life forms were intelligent and not quite the threat they thought they were, General Hammond allowed the organism to spread until O'Neill's body served as a go-between. The creatures agreed to be moved to P4G-881 within the Orb to spread and consume an entire world at their leisure.
Message In a Bottle - SG-1 returns the Orb to Earth with no concept of what it is, or what it represents.