This is a technique I learned over the years from project management gurus to manage time and boost productivity. Instead of letting a task or agenda take as long as it needs to be completed, you set a hard deadline or “time box” for it.
A simple example would be the time limit we have for our daily meetings where we time-boxed it to 10 minutes. This means the meeting can not last more than 10 minutes and if it does, we just end it right away. This is very useful to make sure we don't waste everyone’s time and get straight to the point.
The Pomodoro technique also employs this strategy by time-boxing your task into 25 minutes interval separated by short breaks. (e.g. 3-5 minutes) This teaches you to break tasks into small chunks that can be accomplished within each interval.
Timeboxing has been very useful in software development. The limit forces you to aim for some sort of deliverables when you approach the deadline. It prevents you from spending too much time on a particular task and affects the deliverability of others tasks in the pipeline. The notion of a sprint in Agile/Scrum is basically a timebox of 1-2 weeks.