If this stuff is unfamiliar to you, you should probably read Part I, Day 5 for more details. Objects provide a great way to organize information. First, we deal with real-life objects all the time. A monkey, for example, is an object. Its properties include height, weight, furriness, and sassiness.
All monkeys have the same set of properties.
It's the values of those properties that makes one monkey different from another. Blur does the reverse - try it. JavaScript knows that focus does one thing for a window and something else for a textbox. The idea of focus is the same in both cases, so it makes sense to call it the same thing. Just as you can have the same method do different things for different objects, you can also have the same property mean different things in different objects.