What are logical and physical text styles ?

Logical text styles are general descriptions. Each browser handles a logical style in its own way. Logical styles render the text according to its meaning. For example, <EM> is for emphasizing something and <STRONG> is for strongly emphasizing something.

<STRONG> This is an example of logical text style </STRONG>

Physical text styles indicate the specific type of appearance for a section. For example, bold, italics, underlined etc. They are rendered in the same manner by all browsers.

<B><I> This is an example of physical text style </I></B>