Well what is it? The Knowledge Graph (KG) is actually a box that appears next to the search engine. Not any ordinary box though :)
Google say it's a kind of revolution that they have brought for the search engine. It will contain humongous amount of data that connects places, people and things and their relation with each other. It will lead you to your exact required search that you need to gather information about. It can be used to further enhance your search result.
The Knowledge Graph can understand the difference if the search may have different meanings and accordingly provide you the results that you are looking for.
The knowledge graph will not only provide information about the search you are asking for, but it will also provide information and links about subjects related to the search that you have given in the search box bar. For example, if you search about 'Earth' the planet, it may also give you information about the other planets in the Solar System. They will only refine the search results by analyzing what people are often looking for the same search that people give on the search bar so that you will probably get the desired results only for your search.
This means you can also see key facts about the search that you have given based on the questions other people have asked on the search.
This feature will also be available on smartphones, desktops, laptops so that you can discover more information and other features at the go and at your fingertips.
This will mean less amount of wastage of time and effort for your search and spending the same amount of time for your further analysis. How nice that would be.
The KG provides answers and not just links. A knowledge engine then may be the right word rather than a search engine.
You can look for the demo here.
Watch the video, they make it so good :)