fluid/ liquid

full width of the browser and  automatically resized according to the size of the browser window i.e. no fixed width. in this we do not mentioned CSS Width property  like width: 180px OR WIDTH: 100% ;

This type of width we generally use for fluid layout design

Fixed

It is fixed width and can not resized automatically as fluid like width: 180px ;

while writing CSS  generally use either percentage widths or fixed widths.

This type of width we generally use for fixed layout design