By definition,
SOA governance is the ability to ensure that all of the independent (SOA) efforts (whether in the design, development, deployment, or operations of a service) come together to meet enterprise requirements.
The topic is quite complex and broad in nature and its comprehension might seem a challenge for those new to it. However, for companies looking into serious SOA implementations, Governance is the way to go. Here is a link to an article by the authors of an excellent reference book, which I used in my research. I would highly recommend this for those who want to get started with SOA Governance.