Identity is the philosophical term for what makes something itself, and not something else. For example, Samuel L. Jackson’s identity is what makes Samuel L. Jackson Samuel L. Jackson, and not Nick Fury, Denzel Washington, or LaTanya Richardson. The question is, how do we define that identity? The criteria for identity is more elusive than it might first appear – the obvious criteria often changes depending on what you are trying to differentiate between at the moment.
More broadly, what makes the government of Pennsylvania the government of Pennsylvania? Or a bag of cookies in Entropy THAT bag and not the bag immediately to its left? What makes you you and not someone else? What is it that makes Hillary Clinton at 25 and Hillary Clinton at 45 both Hillary Clinton (née Rodham)?
If you want more information (it’s not at all necessary for the meeting), you can watch a video on identity here.