Physical Tags

Affect appearance of text

BOLD        Bold text <B></B>
BIG         Big Text <BIG></BIG>
BLINK       Blinking text - annoying <BLINK></BLINK>
ITALIC      Italic text <I></I>
SMALL       Small text <SMALL></SMALL>
STRIKE OUT  Text with strike out <STRIKE></STRIKE>
SUBSCRIPT   Text with a subscript <SUB></SUB>
SUPERSCRIPT Text with a superscript <SUP></SUP>
MONOSPACE   Teletype - monospace text <TT></TT>
UNDERLINE   Text wtih underline <U></U>

Logical Tags

Affect content between tags - upto browser to decide how to render 
CITATION  a citation in your document usually rendered as italic
CODE      int width = 5; usually rendered monospace (TT)
EMPHASIS  Some text that is emphasized usually rendered as italic
STRONG    Text having some strong content usually rendered as bold