We have used this field to cover three things
Storyline
The main storyline of the comic book. Usually featured on the front cover or on the inside page
Please just use the first/main story line in this field. If there are other stories you can list them in the Story Description
For example - The storyline for Excalibur (Series One) #12 is:
'The Cross-Time Caper - Part One: My Friends Call Me Billy The Kid!'
Tagline
This is featured on the cover and is usually a quote or a 'headline' if you will - illustrating what is going on inside the comic book
For example:
The tagline for 2000 ad #61 is 'Judge Dredd brings law to...The Cursed Earth'
Subtitle
A good example of when this can be used is in the case of 'Battle' comic book.
Over the years Battle incorporated many other comic books, to keep the data easier to search we have kept the main title as 'Battle' but the subtitle says 'Battle - Action' for when Action comic merged with it. This will help with users searching the database not just for Battle comics, but also for Action comics.