In the absence of a science policy textbook, I would like to ask the scholars of science policy to forgive me for doing an online search for its definition. In fact, I invite them to comment to this post with a more scholarly definition.
In the meantime I have found the following definitions of science policy online. According to wikipedia:
Science policy is an area of public policy concerned with the policies that affect the conduct of the science and research enterprise, including the funding of science, often in pursuance of other national policy goals such as technological innovation to promote commercial product development, weapons development, health care and environmental monitoring [SENSE 1]. Science policy also refers to the act of applying scientific knowledge and consensus to the development of public policies [SENSE 2].
A Royal Society of Chemistry report defines it as:
Science policy is quite a broad term, encompassing not only areas in which science can help achieve policy goals [SENSE 2], but also areas in which policy itself influences science, for instance funding [SENSE 1].