A curious, disparaging term for the human race as it spread out across the galaxy, replicating and filling every available niche. In particular the colour of this particular goo type seems odd to modern ears, since today human baselines (when they can be found) are mostly mid-brown to dark brown in colour. However when the concept of 'goo' was first conceived, in the Information age of Old Earth, many members of the dominant nations at that time apparently had lighter, pinkish skin colours.
Pink Goo is still sometimes used to refer to the Terragen Expansion as a whole, despite the fact that many individuals in the Terragen Sphere are not remotely human.
The term has also been used by vecs and aioid beings of many different kinds as a perjorative term for humanity. The term as used by such non-biological entities is generally taken to refer to the colour of human tissue beneath the skin, and is one of a number of disparaging terms referring to human biology (ref meat-bag, skin-job, crap-machines, meatling, etc.).