You can code individual words or sentences with special styles. Logical styles tag text according to its meaning, while physical styles specify the specific appearance of a section. In the ideal SGML universe, content is divorced from presentation. The other advantage of logical tags is that they help enforce consistency in your documents. The same is true for character styles.
Most browsers render it in bold text.
However, it is possible that a reader would prefer that these sections be displayed in red instead. Logical styles offer this flexibility. Typically displayed in italics. Typically displayed in italics. Typically displayed in italics.