A) Definition
In the context of internet and web browsers, a cookie is a small piece of data sent from a website or an application and stored on the user’s computer or mobile device. It is primarily designed to remember stateful information (such as items added in the shopping cart in an online store), to record the user’s browsing activity or to remember arbitrary pieces of information that the user previously entered into form fields such as names, addresses, passwords and credit card numbers.
Source: based on Wikipedia entry for “HTTP Cookie”