This style is being used more and more, but cannot figure out a proper term to call it.
Constraints: Universal scrollbar, user can scroll from any mouse location in the viewport with the same effect. Each section scrolls in parallel until a section runs out of content, it pins to the bottom of the screen. Scrolling back up, each section's content starts scrolling once the longest page has reached the length of the section content.
Most visible in Facebook with its right-hand notifications and infinite scrolling content. A similar effect is visible on this very StackExchange "ask" page when entering a question: the suggestions scroll until out of space then stay static, the main content continues to scroll.