Hướng dẫn html entities mdn

An HTML entity is a piece of text ["string"] that begins with an ampersand [&] and ends with a semicolon [;]. Entities are frequently used to display reserved characters [which would otherwise be interpreted as HTML code], and invisible characters [like non-breaking spaces]. You can also use them in place of other characters that are difficult to type with a standard keyboard.

Note: Many characters have memorable entities. For example, the entity for the copyright symbol [©] is ©. For less memorable characters, such as — or —, you can use a reference chart or decoder tool.