The Timeline is a special view of Facebook data aggregating all Open Graph events related to you from birth until now. Facebook describes this as: Tell your life story with a new kind of profile.
The Timeline was introduced at the f8 Facebook Developer Conference in 2011. It replaces the previous Facebook profile with an aggregated view of all associated Open Graph events.
The basic idea is to make all Facebook data around one person accessible on a single page. The level of detail changes from high in the recent past to low in the distant past. At any time, the hidden information beyond the current level of detail can be unhidden and made visible. Also, displayed information can be hidden with a click. It is also possible, to define privacy settings on a per-entry basis for the whole timeline.
The result is a curated representation of a person's life with differing content depending on the viewer (and her associated pricacy setting).
The data itself is enriched with Facebook status posts and new Open Graph app data, that can be added to the timeline by a new class of social apps. These apps, once connected, provide not only singular entries (e.g. I just watched a movie) but also data aggregation in a defined way (e.g. these are my favourite movies over time).
Resources:
- Facebook gives an overview right here: http://www.facebook.com/about/timeline