Event represent some sort of action or occurence that happens in the system. Such button click, page load and so on, addEventListener() - These are called event handlers. These are attached to elements that experience this event. It takes 3 parameters - the even type like 'click', the function to be executed after event occurs and optional parameter - True/False for event capturing or bubbling EventListeners stay attached unless explicitly removed. So they are memory heavy. The 'event' object is automatically passed to event handler functions and contains information about the event that occurred. It provides various properties and methods to interact with and control the event. event.target.value refers to the current value of the element that triggered the event.