A more thorough explanation:

Definition: Deceptively suggesting an erroneous origin; fake. Of doubtful or low quality. Archaic. Of illegitimate birth.

• A company selling spurious designer handbags that are not actually made by the designer.
• A website promoting spurious weight loss pills that have not been scientifically proven to work.
• An old law that declared children born out of wedlock to be spurious and therefore ineligible for inheritance.

The examples illustrate how something can be spurious in different ways. The first two examples show how something can be fake or of low quality, while the third example shows how the term can be used in an archaic sense to describe illegitimate birth.