Event bubbling is the process of propagating an event from the innermost element to its parent elements in the DOM hierarchy.

• Events in JavaScript are triggered on elements and then propagate up the DO...read more

its basically the sequence in which the events trigger. like if there is a paragraph nested in a div which is nested in a form, the event on the paragraphs will trigger, then it will go one layer up, and if there are events there, it will trigger, and then on and on. 

https://javascript.info/bubbling-and-capturing

When an event happens on an element, it first runs the handlers on it, then on its parent, then all the way up on other ancestors.

another answer I found: Event bubbling causes all events in the child nodes to be automatically passed to its parent nodes. The benefit of this method is speed because the code only needs to traverse the DOM tree once.