Entity Names
Some characters are used in HTML as code, and if you try to write them as just text, the browser will confuse them with tags and may not display them correctly. For example, the <> characters mean a tag in HTML, so if you want to display them as text, you'd need to use character entities.
"<" is the "less-than tag" and can be written as <. ">" is >, for "greater-than tag". Here's an example, which will show up as "In HTML, the tag defines the beginning of a paragraph.":
<p>In HTML, the <p> tag defines the beginning of a paragraph.</p>
Another such character is , for "non-breaking space". This is a space character that doesn't start a new line. They are commonly used it you want to add more than one space in a row, since HTML will, by default, not display extra spaces.