If you use the less than (<) or greater than (>) signs in your text, the browser might mix them with tags.

Character entities are used to display reserved characters in HTML.

To display a less than sign (<) we must write: &lt; or &#60;

A very uncommon entity in HTML is the non-breaking space: &nbsp;

A diacritical mark is something other than a "glyph" added to a letter.

Some diacritical marks, like grave (  ̀) and acute (  ́) are called accents.

Diacritical marks can appear both above and below a letter, inside a letter, and between two letters.

Diacritical marks can be used in combination with alphanumeric characters to produce a character that is not present in the character set (encoding) used in the page.

Reserved characters in HTML don't have to be replaced with character entities.