what does "*" in the frameset tag actually mean???

Answer 1

Example: <frameset rows="25%,*,25%">
This will create 3 horizontal frames (rows) where the top and bottom one take up 25% space each of the screen. The middle one (*) takes up the rest of the available space.

Frames now belong to the Internet museum :)

Answer 2

For that * is a value like % and px however frameset isnt supported in html5