HTML Tutorial >> HTML Entities.

Characters are used as HTML entities and some combinations of words make an entity, these characters provide a method of entering some predefined words that cannot be expressed or visible in HTML document and these are document's character encoding or that cannot easily be entered on a keyboard. HTML Tutorial will guide you that HTML entities are not case-sensitive but preference is to use small words for HTML entities and these entities specify browser that what to do.
HTML Entity starts with less then sign "<" and ends with grater then sign ">" in between these symbols some predefined words like html title body etc are used to tell browser.

The most common entity in HTML is spaces and these spaces are trimmed by the web browser. And to use the spaces in between text you need to use some special characters as HTML character entities then the spaces will be visible in browser.  Below table is for the explanation of some major entities in HTML.