A cookie(s) in IT terminology refers to small piece of data sent from a server and stored in the user's web browser while the user is browsing. With each subsequent visit to the same server/page, the browser sends this data back to the server. Cookies are normally used to distinguish individual users, user preferences etc. are stored in them.
E-ZAK by itself stores only so called session cookie, which is saved only within the one browser session, and when you close it is deleted (unless browser feature to keep session is used). It is used to enable the system to temporarily remember how the user has set some filters (eg. in the list of contracts), which data he entered into some forms when returning back to edit them (not to be necessary to fill up them again, eg. during registration). It is used to provide a better work with the system.