This question is asking the job seeker to articulate their career goals. What is their vision for themselves in their career in a few years? Many of us have given little thought to this question, or somehow hope that it is something that will sort itself out over time, so long as we work hard and do a good job.
In the past (well, not so long ago really, maybe 10 or 15 years ago) this approach may indeed have been perfectly fine and led to a nice career looking something like this:
So how do you create a vision for yourself? This sounds all high-faluting and a bit 'corporate-speak', but it really means having some idea where you are heading before you set out - which is just common sense really.
In order to start with the end in mind, it pays to spend a bit of time imagining what sort of life you'd like to lead. Do you have loads of ideas of how the library service could be run that you'd love the chance to put into practice? Do you really enjoy mentoring junior members of staff and seeing their skills blossom? Does creating an effective taxonomy or information architecture and seeing users find what they want without having to learn to be 'mini-librarians' to get there bring you great satisfaction?
What sort of job would you need to have in order to do more of these things? Don't worry whether you have the skills, qualifications, experience (or confidence) to do that job right now - just keep it in the back of your mind as you do your skills audit, prepare your CV or sift through job adverts. Think about what the in-between steps might be to help you move in this direction. Evaluate promotions or new jobs against this eventual end goal - will they help you on your way? No? Don't apply for them then, find something more useful.
Some links to posts with other useful ideas and tips around goal-setting:
#Chartership chat on Reflection
Well formed outcomes
Mindtools Personal Goal Setting
Top Achievement's Powerful Written Goals