If your resume contains many short appointments this is an invitation to assuage their fears you'll be out the door the moment you've finished training.
For example, maybe you did a bunch of short-term contract work and they'd like to be reassured that you were there for six months because that's what the client wanted and agreed upfront.
If this job is visibly a diversion from your main passion - like the traditional actor waiting tables between acting gigs - this is a chance to either explain you've changed career directions and this isn't just a filler job for you; or to highlight your relevant experience that will let you get up to speed quickly, so you'll be productive even if you're not with them long.
If your job will involve accumulating knowledge this is a chance to talk about the 'bus factor' and reassure them that you wouldn't dream of hoarding knowledge to make yourself irreplaceable. After all, if you can't be replaced, you can't be promoted!
If you are being hired to give direction to a specific a project that could be done multiple ways this is a chance to tell them about how you love doing things in normal ways, consulting your boss on key decisions, and looking out for the guy that comes after you. You may be the world's greatest expert on underwater basket weaving, but you wouldn't dream of making the project dependent on underwater basket weaving unless it's the best choice for the project, and even then only with your boss's agreement.
If you're being hired for hard-to-hire-for or unique skills they need this is a chance to assure them that your skills aren't entirely unique - while also highlighting that yes, your skills are great, but that's why they should hire you, not why they shouldn't.
If none of the above apply this is a chance to point out you haven't left any of your other jobs after six months, to talk about times you've powered through in the face of temporary adversity and your passion for seeing projects through to completion, and to say that while you might quit a job if it's uniquely terrible, nothing they've told you makes you think this job will be.