The following elements are not in HTML 5 because their effect is purely presentational and their function is better handled by CSS:
basefont
big
center
font
strike
tt
The following elements are not in HTML5 because using them damages usability and accessibility:
frame
frameset
noframes
The following elements are not included because they have not been used often, created confusion, or their function can be handled by other elements:
acronym
is not included because it has created a lot of confusion. Web developers are to use abbr for abbreviations.
applet
has been obsoleted in favor of object.
isindex usage can be replaced by usage of form controls.
dir
has been obsoleted in favor of ul.
See Details W3C