An Introduction to Cookies

Since the introduction of the EU legislative cookie law in 2012, websites that use cookies are required to inform and acquire consent from users that visit a website upon arrival, as part of the ePrivacy Directive.
While a cookie can’t contain viruses, it can carry some sensitive data. Tracking cookies and third party cookies can be used to compile a thorough profile of a user’s’ browsing activities, which is why it is worthwhile knowing what a cookie is and what it does.
A ‘cookie’ is a small piece of data sent from a website and stored in a user’s web browser. Every time a user returns to a website that they have previously visited, the web browser sends the cookie back to the server to notify the website of the user’s previous activity on the website.
Cookies are used to store certain types of information, such as:

Login details
Items in a shopping cart
Information entered into forms
Buttons clicked
Pages visited
How long a user stayed
How often a user returned to the website

Types of cookies

Session cookie – A session cookie is a temporary cookie that will be erased once the user closes their web browser. This type of cookie doesn’t carry an expiry date, which is how the browser knows to delete it.
Persistent cookie – This type of cookie stays on your computer for a set period of time, regardless of whether you close your web browser. This type of cookie would be used to save login details or other preferences for. It can also be referred to as a tracking cookie sometimes, as advertisers can use this type of cookie to record a user’s browsing habits. This can help advertisers tailor adverts to a user’s interests.
Secure cookie – A secure cookie can only be transmitted over a secure, encrypted connection via HTTPS. This is to prevent cookie theft through eavesdropping.
Third-party cookie – A third-party cookie is one that belongs to a different domain than that of the website a user is currently on. These appear when a website has banner advertisements from external websites for example. This allows advertisers to track a user’s browsing history, so that they may offer more specific ads.
To find out more about cookies, click here.
References
https://en.wikipedia.org/wiki/HTTP_cookie