Cookies are the files which are stores in users computer, cookies are designed to store a modest amount of data and the data can be accessed by client or web server.
There are following type of cookies.
1. Session Cookies : Session cookies are basically temporary data files which are based on user's session , When user close the browser these cookies gets deleted and if the same user comes again that website so he again a new user and a new session cookie will be assigned to him.
2. Persistent Cookies : Now if we talk about persistent cookie these are the data files which can be deleted at a specific time duration.may b 3 days or one week or month etc.
3. Secure Cookies : These cookies can be transmitted over a encrypted connection like HTTPS so that it can secure from others.
I think these 4 points are enough to explain in an interview.