In simpler terms - A "Security Pattern" is a reusable design solution to a recurring "security-related" problem.
In a security design process, "Security Patterns" allows to represent a proven solution and helps architects and developers to communicate security knowledge using a common vocabulary and to identify risks that have been traditionally identified only by prototyping experience. The Security patterns can be an architectural solution or a defensive strategy illustrating how a security problem can be resolved.
Adopting Security patterns, depends upon your understanding of security domain, how you identify risks and vulnarabilities in your application design. Before choosing Security patterns, you must follow a Structured Security design methodology that includes risk analysis and trade-off analysis.
For more details, I would suggest you to read the "Free Sample Chapter" and "Patterns Catalog" downloadable from the book Web site.
If you have the book, Refer to Chapters 8 through 14, dedicated for "Security Patterns and Best Practices".