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. Cookies were designed to be a reliable mechanism for websites to remember stateful information or to record the user's browsing activity.
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.