A blob was originally a human that was dumped into a lake near Jersey where radioactive waste gets disposed. The result of this exposure to radioactive waste is the transformation into a large fluid blob-like creature. It is hinted that a blob may consist of multiple people, taking on different characteristics from each person.
Blobs don't have the ability to talk. They require speech synthesizers to communicate with others. They have the same intelligence as normal humans, though.
Although the blobs seem to be essentially liquid, they can maintain a human-like form at will and can even form hands and fingers to press buttons.
- The blobs are most likely a homage to The Blob, a movie featuring a large blob creature devouring everything in its path, similar to the blob seen at the beginning of the Ugly Americans episode "Blob Gets Job".