HTML is used to make web pages more readable. It also has a few special characters used for displaying things like mathematical symbols and copyright symbols.
HTML entities provide a way for web designers/developers to add special characters to an HTML document without using any images or external files. They are supported by all modern web browsers, such as Chrome, Firefox, and Safari.
The process is known as HTML entities encoding/decoding or HTML escape/unescape.
The "&" symbol is used for opening the entity reference while ";" symbol is used for closing the entity reference.