Just a quickie.
Escalations (officially called Expeditions) are sometimes generated after completing an Unrated Complex or (more rarely) a Cosmic Anomaly. They show with a pop-up message and then a bookmark is placed in the Expeditions tab of your Mission Journal. This bookmark is on a timer and expires in 24 hours. If you don’t warp to that bookmark (which is usually 5-10 jumps away) within the timeframe, it will disappear.
(edit 30 April 2014. Sadly, this is no longer true. CCP patched this out sometime in early 2014. You can no longer extend escalations by warping to them)
However, initiating warp to that bookmark extends it by another 24 hours. This can be helpful if you have gotten to the system of the escalation but you don’t have time to do it before it expires – or if based on what is going on in the system you don’t think running it is a good idea right now.