So scenario is that you have a SharePoint 2010 managed metadata term store up and running and you need to make a change to one of the terms. Lets just say that you have spelt one of the terms wrong and need to update it on all items you have added that have selected this misspelt term.
In my example I have a list of countries in the term store and have spelt England wrong and is spelt Egnland.
Jumping a few steps ahead I have a simple list created with a managed metadata property as shown (Noticing the Tag is spelt incorrectly).
So once the item is committed to the list it will look as shown below.
Navigating back to the term store you make an update to the incorrectly spelt term.
After updating and saving the term navigating back to the list you assume that this change should reflect on the list item. Wrong! A timer job needs to be run to update this on list items.
The timer job in question is the Taxonomy Update Scheduler and this runs every hour. You can manually run this timer job from central admin to force an update making sure that you run the timer job associated to the web application where your list is stored.
Once the timer job ran the list automatically updated (within a matter of seconds).