HTML has some special reserved characters e.g. < , > etc. that have special meaning and thus cannot be used freely in the document. But what if we have to display an > or < in the page. For that we can use an corresponding Entity to tell browser to print a < or > to the screen. When the browser parses a HTML document, any word beginning with an & (ampersand) is treated as an Entity which it evaluates and applies the corresponding result to the document as it rendered.
There are some pre-defined Entities defined in HTML specification that the browsers must understand and render HTML accordingly. These can be used for reserved characters or draw special symbols. The following is the list of such entities.