Your online identity is not the same as your real-world identity. Every website you browse, shop from or log on to ‘sees you and your characteristics differently. For instance, when you shop or purchase items, that site begins to establish a partial identity for you or whomever is using your name or identity. So, as each site is visited and viewed, your identity is being added to or enhanced. Birthdate information, favorite color, best friend, whether or not you own a pet, likes, and dislikes are all being collected as your surf and post. Some of this information is under your control; some may not be or may even be invisible to you. All of it contributes to ‘who you are and what you do. This is known as your digital identity.
An identifier is a way of referring to a collection of a person's characteristics or what is described as a partial identity or persona. Many websites and search engines maintain information about your identity. They then assign you an identifier and store it in your web browser as a cookie. That cookie links together all of your characteristics creating your identity. In other words, it tags you. Some of them may match your real identity and some may not.