Definition:
HTML, CSS and JavaScript templates/frameworks.
 
Three types:
1. Developer-centric pattern, focus on quick code production turnover.
2. Designer-centric pattern, emphasise problem solving through general UI recommendations.
3. Combination of 1 & 2, allowing developers and designers to work in tandem, CSS frameworks like Foundation or Bootstrap.
 
When to use:
When you have multiple teams working on a suite of products and each team is doing Rapid prototyping on a different product.