This is a term from the (software) project management area. It basically means that deliverables are not fix in terms of content, which is the “normal” approach. The latter means that something has been agreed-upon as scope and will be delivered when that has scope has been implemented. Hopefully the planned deadline will be met, but it can be sacrificed in order to deliver the full thing. With time boxing, however, one is willing to reduce the scope in order to meet a deadline (goes hand-in-hand with the MoSCoW method). You therefore often find it in the following contexts
- Agile projects
- “Political” projects where it is more important to keep a date than functionality
For a more thorough discussion check out this article.